Setting up z/OS for TLS clients

There is a lot of configuration needed when setting up TLS(SSL) between a server and a client. There are many options and it is easy to misconfigure. The diagnostic information you get when the TLS handshake fails is usually insufficient to identify any problems.

You need the following on z/OS:

  • One or more Certificate Authority certificates. You can create and use your own for testing. If you want to work with external sites you’ll need a proper (external) CA, but for validation and proof of concept you can create your own CA. You could set up a top level CA CN=CA,O=MYORG, and another one (signed by CA=CA,O=MYORG), called CN=CA,OU=TEST,O=MYORG. Either or both of the public CA certificates will need to be sent to the clients in imported into their keystore.
  • A private/public key, signed by a CA, (such as signed by CA=CA,OU=TEST,O=MYORG).
  • The private key is associated with a userid.
    • The signing operation takes the data (the public key), does a hash sum calculation on the data, encrypts this hash sum, and stores the encrypted hash value, and CA public certificate with the original data. To check the signature, the receiving application compares the CA with its local copy, if that matches, does the same checksum calculation, decodes the encrypted hash sum – and checks the decrypted and locally calculated values match.
    • A certificate is created using one from a list of algorithms. (For example, Elliptic Curve, RSA). When the certificate is sent to the client, the client needs to support the algorithm. Either end can be configured, for example, to support Elliptic Curve, but not RSA.
  • A keyring to contain your private key(s) – this can also contain CA public certificates of the partners (clients or servers).
  • A “site” keyring (public keystore, or trust ring) which holds the public CA certificates of all the other sites you work with. If you have only one keyring per user or application, you need to update each of them if you need to an a new CA to your environment. Many applications are only designed to work with one keyring. Java applications tend to have a key store(for the private key) and a trust store for the CAs.
  • Some applications can support more than one private certificate on a keyring. The certificate needs to match what the client can support.
  • For certificates which are sent to your server, you need a copy of the CA(s) used to sign the incoming certificate. If you have a copy of the CA, then you can validate any certificate that the CA signed. This means you do not have to have a copy of the public certificate of every client. You just need the CA.
    • Some application need access to just one CA in the chain, other applications need access to all certificates in the CA chain.
  • As part of the TLS handshake
    • the client sends up a list of the valid cipher specs it supports (which algorithms, and size of key)
    • the server sends down a subset of the list of cipher spec to use (from the client’s list)
    • the server can also send down its certificate, which contains information such as the distinguished name CN=zSERVER, OU=TEST, O= MYORG, and host name.
    • the client can validate these names – to make sure the host name in the certificate matches the host, and what it was expecting.
    • if requested, the client can send up its certificate for identification. The server can validate the certificate, and can optionally map it to a userid on the server.
  • A userid can be given permission to read certificate in another user’s keyring. A userid needs a higher level of authority to be able to access the private key in another id’s keyring.

Create the Certificate Authority

//IBMRACF  JOB 1,MSGCLASS=H                               
//S1  EXEC PGM=IKJEFT01,REGION=0M                         
//SYSPRINT DD SYSOUT=*                                    
//SYSTSPRT DD SYSOUT=*                                    
RACDCERT certauth LIST(label('DOCZOSCA')) 
RACDCERT GENCERT  -                                         
  CERTAUTH -                                                
             O('COLIN') -                                   
             OU('CA')) - 
  NOTAFTER(   DATE(2027-07-02  ))-                          
  KEYUSAGE(   CERTSIGN )  -      
  SIZE(2048) -                                              

This certificate is created against “user” CERTAUTH. Keyusage CERTSIGN means it can be used to sign certificates. “user” CERTAUTH is often displayed internally as “irrcerta”.

Once it has been created the certificate should be connected to every ring that may use it, see below.

Export the CA certificate to a file so, clients can access it


The file looks like

-----BEGIN CERTIFICATE-----                                        

This can be sent to the clients, so they can validate certificates sent from the server. This file could be sent using cut and paste, or FTP.

Create the keyring for user START1.

The instructions below lists the ring first – in case you need to know what it was before you deleted it”



RACDCERT ADDRING(TN3270) ID(START1)                                                          


Connect the CA to every keyring that needs to use it

                            CERTAUTH LABEL('DOCZOSCA'))

Create a user certificate and sign it on z/OS

This creates a certificate and gets is signed – as one operation. You can create a certificate, export it, sent it off to a remote CA, import it, and add it to a userid.

RACDCERT ID(START1) GENCERT -                                   
             O('NISTECC521') -                                  
             OU('SSS')) -                                       
   SIZE(521) - 
   SIGNWITH (CERTAUTH LABEL('DOCZOSCA')) -                      
   WITHLABEL('NISTECC521')     -                                

RACDCERT ID(START1) CONNECT(RING(TN3270) -                      
                            ID(START1)  -                       
                            DEFAULT  - 
                            LABEL('NISTECC521') )               
SETROPTS RACLIST(DIGTCERT,DIGTRING ) refresh                    
RACDCERT LIST(LABEL('NISTECC521' )) ID(START1)                  
RACDCERT LISTRING(TN3270)  ID(START1)                           

This creates a certificate with type Elliptic Curve (NISTECC) with a key size of 521. It is signed with the CA certificate created above.

The ALTNAME, is a field the client can verify that the Source Name in the certificate matches the IP address of the connection.

It is connected to the user’s keyring as the DEFAULT. The default certificate is used if the label of a certificate is not specified when using the keyring.

Give a user access to the keyring

    ID(COLIN )  ACCESS(UPDATE )                          
SETROPTS RACLIST(RDATALIB) refresh                       
  • Update access give userid COLIN access to the private key.
  • Read access only gives access to the public keys in the ring.

You would typically give a group of userids access, not just to individual userids.

Import the client’s CA’s used to sign the client certificates

This is the opposite to Export the CA certificate to a file so clients can access it above.

Copy the certificate to z/OS. This can be done using FTP or cut and paste.

Use it!

I used it in AT-TLS

TTLSConnectionAdvancedParms       TNCOonAdvParms 
 ServerCertificateLabel  NISTECC521
TTLSSignatureParms                TNESigParms 
   CLientECurves Any 
TTLSEnvironmentAction                 TNEA 
  HandshakeRole                       ServerWithClientAuth 
    Keyring                   start1/TN3270 

Write instructions for your target audience – not for yourself.

Over the last couple of weeks, I’ve been asked questions about installing two products on z/OS. I looked at the installation documentation, and it was written the way I would write it for myself – it was not written for other people to follow.

I sent some comments to one of the developers, and as the comments mainly apply to the other products as well, I thought I would write them down – for when another product comes along.

I’ve been doing some documentation of for AT-TLS which allows you to give applications TLS support, without changing the application, so I’ll focus on a product using TCP/IP.

What is the environment?

The environment can range from one person running z/OS on a laptop, to running a Parallel Sysplex where you have multiple z/OS instances running as a Single System Image; and taking it further, you can have multiple sites.

What levels of software

Within a Sysplex you can have different levels of software, for example one image at z/OS 2.4 and another image at z/OS 2.5 You tend to upgrade one system to the next release, then when this has been demonstrated to be stable, migrate the other systems in turn.

Within one z/OS image you can have multiple levels of products, for example MQ 9.2.3 and MQ 9.1. People may have multiple levels so they test the newer level, and when it looks stable, they switch to the newer level and later remove the older level. If the newer level does not work in production – they can easily switch back to the previous level.

Each version may have specific requirements.

  • If your product has an SVC, you may need an SVC for each version, unless the higher level SVC supports the lower level code.
  • If your product uses a TCP/IP port, you will need a port for each instance.

You need to ensure your product can run in this environment, with more than one version installed on an image.

How do things run?

Often z/OS images and programs run for many months. For example IPLing every three months to get the latest fixes on. Your product instance may run for 3 months before restarting. If you write message to the joblog, or have output going to the JES2 spool, you want to be able to purge old output without shutting down your instance. You can specify options to “spin” off output and make the file purge-able.

Your instance may need to be able to refresh its parameters. For example, if a key in a keyring changes, you need to close and reopen the keyring. This implies a refresh command, or the keyring is opened for each request.

Who is responsible for the system?

For me – I am the only person using the system and I am responsible for every thing.

For big systems there will be functions allocated to different departments:

  • Installation of software (getting the libraries and files to the z/OS image)
  • The z/OS systems team – creating and updating the base z/OS system
  • The Security team – this may be split into platform security(RACF), and network security
  • Data management – responsible for data, backup (and restore), migration of unused data sets to tape, ensuring there is enough disk space available.
  • Communications team – responsible for TCPIP connectivity, DNS, firewalls etc.
  • Database team – responsible for DB2 and other products
  • Liberty and z/OSMF etc built on top of Liberty.
  • MQ – responsible for MQ, and MQ to MQ connectivity.

Some responsibilities could be done by different teams, for example creating the security profile when creating a started task. This is a “security” task – but the z/OS systems programmer will usually do it.

How are systems changes managed?

Changes are usually made on a test system and migrated into production. I’ve seen a rule “nothing goes into production which has not been tested”. Some implications of this are

  • No changes are typed into production. A file can be copied into production, and a file may have symbolic substitution, such as SYSTEM=&SYSNAME. You can use cut and paste, but no typing. This eliminates problems like 0 being misread as O, and 1,i,l looking similar.
  • Changes are automated.
  • Every change needs a back-out process – and this back-out has been tested.
    • Delete is a 2 phase operation. Today you do a rename rather than a delete; next week you do the actual delete. If there is a problem with the change you can just rename it back again. Some objects have non obvious attributes, and if you recreate an object, it may be different, and not work the same way as it used to.

There are usually change review meetings. You have to write a change request, outlining

  • the change description
  • the impact on the existing system
  • the back-out plan
  • dependencies
  • which areas are affected.

You might have one change request for all areas (z/OS, security, networking), or a change request for each area, one for z/OS, one for security, one for networking.

Affected areas have to approve changes in their area.

How to write installation instructions

You need to be aware of differences between installing a product first time, and successive times. For example creating a security definition. It is easy to re-test an install, and not realise you already have security profiles set up. A pristine new image is great for testing installation because it is clean, and you have to do everything.

Instructions like

  • Task 1 – create sys1.proclib member
  • Task 2 – define security profile
  • Task 3 – allocate disk storage
  • Task 4 – define another security profile
  • Task 5 – update parmlib

may make sense when one person is doing the work, but not if there are many teams.

It is better to have a summary by role like

  • z/OS systems programmer
    • create proclib member
    • update parmlib
  • Security team
    • Define security profile 1
    • Define security profile 2
  • Storage management team
    • Allocate disk space

and have links to the specific topics. This way it is very clear what a team’s responsibilities are, and you can raise one change request per team.

This summary also gives a good road map so you can see the scale of the installation task.

It is also good to indicate if this needs to be done once only per z/OS image, or for every instance. For example

  • APF authorise the load libraries – once per z/OS image
  • Create a JCL procedure in SYS1.PROCLIB – once per instance

Some tasks for the different roles

z/OS system programmers

  • Create alias for MYPROD.* to a user catalog
  • APF authorise MYPROD…. datasets
  • Create PARMLIB entries
  • Update LNKLST and LPA
  • Update PROCLIB concatenation with product JCL
  • Create security profiles for any started tasks; which userid should be used?
  • WLM classification of the started task or job.
  • Schedule delete of any old log files older than a specified criteria
  • When multiple instances per LPAR, decide whether to use S MYSTASK1, S MYSTASK2, or S MYSTASK.T1, S MYSTASK.T2
  • Do you need to specify JESLOG SPIN to allows JES2 logs to be spun regulary, or when they are greater than a certain size, or any DD SYSOUT with SPIN?
  • ISPF
    • Add any ISPF Panels etc into logon procedures, or provide CLIST to do it.
    • Update your ISPF “extras” panel to add product to page.
  • Try to avoid SVCs. There are better ways, for example using authorized services.
  • Propagate the changes to all systems in the Sysplex.
  • What CF structures are needed. Do they have any specific characteristics, such as duplexed?
  • How much (e)CSA is needed, for each product instance.
  • Does your product need any Storage Class Memory (SCM).

Security team

  • Create groups as needed eg MYPRODSYS, MYPRODRO, and make requester’s userid group special, so they can add and remove userids to and from the groups.
  • Create a userid for the started task. Create the userid with NOPASSWORD, to prevent people logging on with the userid and password.
  • Protect the MYPROD.* datasets, for example members of group MYPRODSYS can update the datasets, members of group MYPRODRO only have read-only access.
  • Create any other profiles.
  • Create any certificate or keyrings, and give users access to them.
  • Set up profiles for who can issue operator commands against the jobs or procedures.
  • Does the product require an “applid”. For example users much have access to a specific APPL to be able to use the facilities. An application can use pthread_security_applid_np, to change the userid a thread is running on – but they must have access to an applid. The default applid is OMVSAPPL.
  • Do users needing to use this product need anything specific? Such as id(0), needing a Unix Segment, or access to any protected resources? See below for id(0).
  • If a client authenticates to the server, the server needs access to BPX.SERVER in the RACF FACILITY.
  • The started task userid may need access to BPX.DAEMON.
  • If a userid needs access to another user’s keyring, the requestor needs read access to user.ring.LST in CLASS(RDATALIB) or access to IRR.DIGTCERT.LISTRING.
  • If a userid needs access to a private key in a keyring the requester needs If a userid needs access to another user’s keyring, the requester needs control access to user.ring.LST in CLASS(RDATALIB).
  • You might need to program control data sets, for example RDEF PROGRAM * ADDMEM(‘SYS1.LINKLIB’//NOPADCHK) UACC(READ) .
  • Users may need access to ICSF class CSFSERV and CSFKEYS.
  • Use of CLASS(SURROGAT) BPX.SRV.<userid> to allow one userid to be a surrogate for another userid.
  • Use of CLASS(FACILITY) BPX.CONSOLE to remove the generation of BPXM023I messages on the syslog.

Storage team

  • How much disk space is needed once the product has been installed, for data sets, and Unix file systems. This includes product libraries and instance data, and logs which can grow without limit.
  • How much temporary space is needed during the install.
  • Where do Unix files for the product go? for example /opt/ or /var….
  • Where do instance files go. For example on image local disks, or sysplex shared disks. You have an instance on every member of the Sysplex – where you do put the instance files?
  • How much data will be produced in normal running – for example traces or logs.
  • When can the data be pruned?
  • Does the product need its own ZFS for instance data, to keep it isolated and so cannot impact other products.
  • Are any additional Storage Classes etc needing to be defined? These determine if and when datasets are migrated to tape, or get deleted.
  • Are any other definitions needed. For example for datasets MYPROD.LOG*, they need to go on the fastest disks, MYPROD.SAMPLES* can go on any disks, and could be migrated.

Database team

  • What databases, tables,indexes etc are required?
  • How much disk space is needed.
  • What volume of updates per second. Can the existing DB2 instances sustain the additional throughput?
  • What security and protection is needed at the table level and at the field level.
  • What groups are permitted to access which fields?
  • What auditing is needed?
  • Is encryption needed?


  • Do you need to uses MQ Shared Queue between queue managers?
  • How much data will be logged per second?
  • What is the space needed for the message storage, disk space, buffer pool and Coupling Facility?
  • Product specific definitions.
  • Security protection of any product specific definitions.


  • Which port(s) to use?
    • Do you need to control access to ports with the SAF resource on the PORT entry, and permit access to profile EZB.PORTACCESS.sysname.tcpname.resname
  • Use of Sysplex Distributor to route work coming in to a Sysplex to any available system?
  • Update the port list – so only specific job can use it
  • RACF profile for port?
  • Which cipher specs
  • Which level of TLS
  • Which certificates
  • Any AT-TLS profile?
  • Any firewall changes?
  • Any class of service?
  • Any changes to syslogd profile?
  • Are there any additional sites that will be accessed, and so need adding to the “allow” list.


  • If the started tasks, or jobs need to be started at IPL, create the definitions. Do they have any pre-reqs, for example requiring DB2 to be active.
  • If the jobs are shutdown during the day, should they be automatically restarted?
  • Add automation to shut down any jobs or started tasks, when the system is shutdown
  • Which product messages need to be managed – such as events requiring operator action, or events reported to the site wide monitoring team.


  • Play book for product, how to start, and stop it
  • Are there any other commands?


  • Any SMF data needed to be collected.
  • Any other monitoring.
  • How much additional CPU will be needed – at first, and in the long term.

Making your product secure

Many sites are ultra careful about keeping their system secure. The philosophy is give a user access for what they need to do – but no more. For example

  • They will not be comfortable installing a non IBM SVC into their system. An SVC can be used from any address space, so if there is any weakness in the SVC it could be exploiter.
  • Using id(0) (superuser) in Unix Services is not allowed. The userid needs to be given specific permission. If the code “changes userid” then services like pthread_security_applid_np() should be used; where the applid is part of the configuration. Alternatives include __login_applid. End users of this facility will need read access to the specific applid.


If you are using TLS there are other considerations

  • Any certificate you generate needs a long validity date, and JCL to recreate it when it expires.
  • If you create a Certificate Authority you need to document how to export it and distribute it to other platforms
  • Browsers and application may verify the host name, so you need to generate a certificate with a valid name. The external z/OS name may be different from the internal name.
  • You should support TLS V1.2 and TLS 1.3 Other TLS and SSL versions are deprecated.
  • It is good practice to have one keyring with the server certificate with its private key, and a “common” trust store keyring which has the Certificate Authorities for all the sites connecting to the z/OS image. If you connect to a new site, you update the common keyring, and all applications pick up the new CA. If you have one keyring just for your instance, you need to maintain multiple keyrings when a new certificate is added, one for each application.

How do I trace TCP/IP sockets on z/OS?

I stumbled on this by accident.

In the TCPIP.DATA configuration file you can specify


I copied the configuration file, and made the change. I used it in my JCL


Note if you use TRACE SOCKET in the configuration file used by every one – then every one will get their sockets traced – which may not be what you want.

The output to SYSPRINT is like

request = HCreate                                                                         
EZY3829I  pre   0xe3e2d9c2 00c00001 00010000 00000020 e3c3d7c9 d7404040 00000000 00000000 
EZY3830I        0x00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 
EZY3831I        0x00000000 1fa77318 00000000 00000000 00000000 00000080 00000000 00000000 
EZY3832I        0x00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 
EZY3833I        0xffff0002 00000000 00000000 40404040 40404040 f18681f7 f68686f8 00000000 
EZY3834I        0x00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 
request = HCreate                                                                         
EZY3835I  post  0xe3e2d9c2 00c00001 00010000 00000020 e3c3d7c9 d7404040 00000000 00000000 
EZY3830I        0x7f5ec0f0 00010000 00000000 00000000 00000000 00000000 00000000 00000000 
EZY3831I        0x00000000 1fa77318 00000000 00000000 00000000 00000080 00000000 00000000 
EZY3832I        0x00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 
EZY3833I        0xffff0002 00000031 00000000 40404040 40404040 f18681f7 f68686f8 00000000 
EZY3834I        0x00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 

These messages and the content are not documented – they are for IBM Software Support.

Compiling the TCP/IP samples on z/OS

Communications server (TCPIP) on z/OS provides some samples. I had problems getting these to compile, because the JCL in the documentation was a) wrong and b) about 20 years behind times.


There are some samples in TCPIP.SEZAINST

  • TCPS: a server which listens on a port
  • TCPC: a client which connects to a server using IP address and port
  • UDPC: C socket UDP client
  • UDPS: C socket UDP server
  • MTCCLNT: C socket Multitasking client
  • MTCSRVR: C socket Multitasking server
  • MTCCSUB: C socket subtask MTCCSUB

The JCL I used is

//       CPARM='OPTFILE(DD:SYSOPTF),LSEARCH(/usr/include/)', 
//               DD 
RENT ILP32        LO 
// PARM='4000          ' 

Change the source

The samples do not compile with the above JCL. I needed to remove some includes

#include <manifest.h> 
// #include <bsdtypes.h> 
#include <socket.h> 
#include <in.h> 
// #include <netdb.h> 
#include <stdio.h> 

With the original sample I got compiler messages

ERROR CCN3334 CEE.SCEEH.SYS.H(TYPES):66 Identifier dev_t has already been defined on line 98 of “TCPIP.SEZACMAC(BSDTYPES)”.
ERROR CCN3334 CEE.SCEEH.SYS.H(TYPES):77 Identifier gid_t has already been defined on line 101 of “TCPIP.SEZACMAC(BSDTYPES)”.
ERROR CCN3334 CEE.SCEEH.SYS.H(TYPES):162 Identifier uid_t has already been defined on line 100 of “TCPIP.SEZACMAC(BSDTYPES)”.
ERROR CCN3334 CEE.SCEEH.H(NETDB):87 Identifier in_addr has already been defined on line 158 of “TCPIP.SEZACMAC(IN)”.

INFORMATIONAL CCN3409 TCPIP.SEZAINST(TCPS):133 The static variable “ibmcopyr” is defined but never referenced.

I tried many combinations of #define but could not get it to compile, unless I removed the #includes.

Compile problems I stumbled upon

Identifier dev_t has already been defined on line ...                                                     
Identifier gid_t has already been defined on line ...                                                     
Identifier uid_t has already been defined on line ....

This was caused by the wrong libraries in SYSLIB. I needed


The compile problems were caused by CEE.SCEEH.SYS.H being missing.

Execution problems

I had some strange execution problem when I tried to use AT-TLS within the program.

EDC5000I No error occurred. (errno2=0x05620062)

The errno2 reason from TSO BPXMTEXT 05620062 was

BPXFSOPN 04/27/18
JRNoFileNoCreatFlag: A service tried to open a nonexistent file without O_CREAT

Action: The open service request cannot be processed. Correct the name or the open flags and retry the operation.

Which seems very strange. I have a feeling that this field is not properly initialised and that this value can be ignored.

Colin’s “TCPIP on z/OS” message explanations


This blog post is a repository of my interpretation of the messages from the Z/OS communications server family of products. Ive tried to add more information, or explain what some of the values are. it is aimed at search engines, not as a readable article.


This message can come from

  • OSPF external advertisements : The DISPLAY TCPIP,tcpipjobname,OMPROUTE,OSPF,EXTERNAL
  • OSPF area link state database: The DISPLAY TCPIP,tcpipjobname, OMPROUTE, OSPF, DATABASE, AREAID=area-id



  1. Router links advertisement
  2. Network links advertisements
  3. Network summaries
  4. Autonomous System(whole network) summaries
  5. Autonomous System(whole network) external advertisements (DISPLAY TCPIP, tcpipjobname, OMPROUTE, OSPF,EXTERNAL)


I got this with

ROUTE 2001:db8::7/128 host 2001:db8:1::3    IFPORTCP6      MTU 5000 

Which has a first hop address! The problem was /128. Remove this and it worked. If you then issue TSO NETSTAT ROUTE it gives

DestIP:   2001:db8::7/128 
  Gw:     2001:db8:1::3 
  Intf:   IFPORTCP6         Refcnt:  0000000000 
  Flgs:   UGHS              MTU:     5000 

EZZ7904I Packet authentication failure, from, type 2

An OSPF packet of the specified type was received. The packet fails to authenticate.

System programmer response

Verify the authentication type and authentication key specified for the appropriate interfaces on this and the source router. The types and keys must match in order for authentication to succeed. If MD5 authentication is being used and OMPROUTE is stopped or recycled, ensure that it stays down for at least 3 times the largest configured dead router interval of the OSPF interfaces that use MD5 authenticaiton, in order to age out the authentication sequence numbers on routers that did not recycle.

Types are

  • 0 Null authentication
  • 1 Simple password
  • 2 Cryptographic authentication

See OSPF Version 2.

From the message description, this could be a timing issue.

EZZ7921I OSPF adjacency failure, neighbor, old state 128, new state 4, event 10


I got this restarting frr on Linux.

The Neighbor State Codes can be one of the following:

  • 1 Down
  • 2 Attempt
  • 4 Init (session has (re) started
  • 8 2-way
  • 16 ExStart
  • 32 Exchange
  • 64 Loading
  • 128 Full. the router has sent and received an entire sequence of Database Description Packets.

The Neighbor Event Codes can be one of the following:

  • 7 SeqNumberMismatch
  • 8 BadLSReq
  • 10 1-way. An Hello packet has been received from the neighbor, inwhich this router is not mentioned. This indicates that communication with the neighbor is not bidirectional. For example the remote end is restarting.
  • 11 KillNbr
  • 12 InactivityTimer
  • 13 LLDown
  • 15 NoProg. This event is not described in RFC1583. This is an indication that adjacency establishment with the neighbor failed to complete in a reasonable time period (Dead_Router_Interval seconds). Adjacency establishment restarts.
  • 16 MaxAdj. This event is not described in RFC2328. This indicates that OMPROUTE has exceeded the futile neighbor state loop threshold (DR_Max_Adj_Attempt). Even if a redundant parallel interface (primary or backup) exists, OMPROUTE continues to attempt to establish adjacency with the same neighboring designated router over the existing or alternate interface.

EZZ7905I No matching OSPF neighbor for packet from, type 4

  • EZZ7905I No matching OSPF neighbor for packet from, type 4
  • EZZ7904I Packet authentication failure, from, type 2

I got these when I was using OSPF Authentication_type=MD5, and the Authentication_Key_ID did not match.


You get messages prefixed by this message if SYSLOGD is not running.

For example

BPXF024I (TCPIP) Oct 6 10:11:10 omproute 67174435 : EZZ8100I OMPROUTE subagent Starting

With the SYSLOGD running you get



EZZ6035I TN3270 DEBUG CONN DETAIL 1035-00 Policy is invalid for the conntype specified.

RCODE: 1035-00 Policy is invalid for the conntype specified.


The AT-TLS policy needs

  ApplicationControlled         On 

Now you know, it is obvious that APPLCNTRL in the message means ApplicationControlled!


EZZ6035I TN3270 DEBUG CONN   DETAIL                      
  RCODE: 1035-00  Policy is invalid for the conntype specified.      
  PARM1:          PARM2: SECURE   PARM3: NO POLICY                   

There is no AT-TLS policy for the port being used. The message does not tell you which port or policy is being used. The operator command “D TCPIP,TN3270,PROFILE” shows which ports are in use.

EZZ6060I TN3270 PROFILE DISPLAY 968                            
  L******  ***TSBTQ***RT*  TJ*  TSTTTT**TT  IP**STT  SMD*      
----- PORT:  2023  ACTIVE           PROF: CURR CONNS:      0   

The TS under security mean TLS connection, Secure Connection.

Use the Unix commands pasearch -t 1>a oedit a to display the configuration and search for “port”. The port value may be specified – or it may be within a range.

LocalPortFrom: 2023 LocalPortTo: 2025

EZZ6035I TN3270 RCODE: 1030-01 TTLS Ioctl failed for query or init HS.

PARM1: FFFFFFFF PARM2: 00000464 PARM3: 77B77221

The PARM1 value is the return value, the PARM2 value is the return code, and the PARM3 value is the reason code for the ioctl failure; these values are defined in z/OS UNIX System Services Messages and Codes.

  • Error numbers. 464 is ENOTCONN:The socket is not connected
  • Reason codes 7221: The connection was not in the proper state for retrieving.

I got this when

  • there was problems with the System SSL configuration, such as invalid certificate name,
  • when the z/OS certificate was not suitable eg the key needed to be bigger
  • the HandshakeRole ServerWithClientAuth was specified – it should be HandshakeRole Server .

EZZ6035I TN3270 DEBUG CONFIG EXCEPTION RCODE: 600F-00 System SSL initiation failed.


AT-TLS did not have access to the keyring. For example need access to

tso setropts refresh raclist(rdatalib)

and perhaps access to


1030-02 – also to do with keyrings.

RCODE: 1016-01 Port Task setup failed.
PARM1: 0000102B PARM2: 00000BCF PARM3: 00000000

This was caused by

   3023 TCP *   SAF     VERIFY 

and getting


Define the profiles and give the userid access to it.


EZZ7815I Socket 11 bind to port 521, address :: failed, errno=111:EDC5111I Permission denied., errno2=74637246

This was caused by

   520 UDP OMPROUTE            ; RouteD Server 
   521 UDP OMPROUTE            ; RouteD Server for IP V6 

The name after the UDP (OMPROUTE) did not match my job name which was trying to use it.

EDC5111I Permission denied. errno2=0x744C7246.

0x744C7246 744C7246. This problem occurred with using port 22 (Telnet).

Changing to port 2222 showed that it was just port 22, the other configuration worked.

Commenting out the RESTRICTLOWPORTS and the PORT reservation for “22 SSHD” showed it was one of those.

Using the RESTRICTLOWPORTS parameter to control access to unreserved ports below port 1024 (an application cannot obtain a port in the range 1 – 1023 that has not been reserved by a PORT or PORTRANGE statement, unless the application is APF-authorized or has OMVS superuser [UID(0)] authority).

The solution was to use port reservation such as

    22 TCP SSHD* NOAUTOLOG  ; OpenSSH SSHD server



I had RESOLVER_CONFIG=//’ADCD.Z24C.TCPPARMS(TCPDATA)’ pointing to an invalid data set.

OSPF on z/OS, basic commands

This article follows on from getting the simplest example of OSPF working. It gives the z/OS commands to display useful information.

I want to


I configured multiple TCPIP subsystems, and each one had an OMPROUTE defined. I used a started task OEMP1, as the OMPROUTE for my base TCPIP.

If you have only one TCPIP subsystem, you can use OMPROUTE as your name.

F OMP1,OSPF,areasum

This displays the area summary.

AREA ID        AUTHENTICATION   #IFCS  #NETS  #RTRS  #BRDRS DEMAND           NONE              2      3      3      0  OFF        


EZZ7853I AREA LINK STATE DATABASE                        
                # ADVERTISEMENTS:       0                     
                CHECKSUM TOTAL:         0X0                   

F OMP1,ospf,list,areas

“Displays all information concerning configured OSPF areas and their associated ranges.”

 AREA ID          AUTYPE          STUB? DEFAULT-COST IMPORT-SUMMARIES?          0=NONE           NO          N/A           N/A 
 AREA ID          ADDRESS          MASK             ADVERTISE?    YES 

The entry with address comes from the omproute configuration file entry

range ip_address= 

F OMP1,ospf,list,ifs

“For each OSPF interface, display the IP address and configured parameters as coded in the
OMPROUTE configuation file”

 IP ADDRESS      AREA             COST RTRNS TRDLY PRI HELLO  DEAD DB_EX             1     5     1   1    10    40    40             1     5     1   1    10    40    40 

F OMP1,ospf,list,nbma

“Displays the interface address and polling interval related to interfaces connected to nonbroadcast multiaccess networks.”


F OMP1,ospf,list,nbrs

“Displays the configured neighbors on non-broadcast networks”


“Displays all virtual links that have been configured with this router as an endpoint.”

F OMP1,ospf,database,areaid=

EZZ7853I AREA LINK STATE DATABASE                           
  1           0X80000013   61  0X3D8D    
  1           0X8000001A  393  0X5A78    
  1 @         0X8000000D  286  0X9E22    
  2          0X80000006 1241  0XC35E    
  2          0X80000003  353  0X8197    
  2 @         0X80000005 3600  0X64BD    
  2          0X80000003  383  0X6BAB    
  2 @         0X80000005 3600  0X4ED1    

(LS) Type is described here.

  1. Router links advertisement
  2. Network link advertisement
  3. Summary link advertisement
  4. Summary ASBR advertisement
  5. Autonomous System (AS -think entire network) external link.
  • LS ORIGINATOR: Indicates the router that originated the advertisement.
  • LS DESTINATION: Indicates an IP destination (network, subnet, or host).

From the above


means router told every one that it has the end of a network link, and its address is


says router told every one “here I am, router”.

You can use the type and destination in the command:


For example



This allows you to see a lot of information about an individual element of the OSPF database.

LSTYPE=1 is for Router Links Advertisment.

The valid LSID values are given in the output of F OMP1,ospf,database,areaid= above.

  LS DESTINATION (ID):                     
  ROUTER TYPE:      (0X00)                         
  # ROUTER IFCS:   3                        
    LINK ID:        
    LINK DATA:        
    INTERFACE TYPE:   2               
    LINK ID:        
    LINK DATA:        
    INTERFACE TYPE:   2               
    LINK ID:        
    LINK DATA:        
  • LINK ID: Is the IP address of the remote end
  • LINK DATA: Is the IP address of the router’s end
  • INTERFACE TYPE: 2 is “Network links”.


This allows you to see a lot of information about an individual element of the OSPF database.

LSTYPE=2 is “Network links the set of routers attached to a network”.

The valid LSID values are given in the output of F OMP1,ospf,database,areaid= above, with type=2.

F OMP1,OSPF,LSA,LSTYPE=2,LSID=                     
EZZ7880I LSA DETAILS                                   
LS OPTIONS:      E (0X02)                          
LS TYPE:         2                                 
LS DESTINATION (ID):                      
LS ORIGINATOR:                           
NETWORK MASK:                     
 ATTACHED ROUTER:          (100)    
 ATTACHED ROUTER:          (100)    

Where (100) is the metric.

F OMP1,ospf,if

 IFC ADDRESS     PHYS         ASSOC. AREA     TYPE   STATE  #NBRS  #ADJS        JFPORTCP4         BRDCST   64      1      1        ETH1         BRDCST   64      1      1 

F OMP1,ospf,neighbor

 NEIGHBOR ADDR   NEIGHBOR ID     STATE  LSRXL DBSUM LSREQ HSUP IFC           128      0     0     0  OFF JFPORTCP4           128      0     0     0  OFF ETH1 

F OMP1,ospf,routers


F OMP1,ospf,statistics

                 OSPF ROUTER ID: (*OSPF) 
                 EXTERNAL COMPARISON:    TYPE 2 
                 AS BOUNDARY CAPABILITY: NO 
 ATTACHED AREAS:                  1  OSPF PACKETS RCVD:             3336 
 TRANSIT NODES FREED:            78  LS ADV. ALLOCATED:                1 
 LS ADV. FREED:                   1  QUEUE HEADERS ALLOC:             32 
 QUEUE HEADERS AVAIL:            32  MAXIMUM LSA SIZE:               512 
 # DIJKSTRA RUNS:                 4  INCREMENTAL SUMM. UPDATES:        0 
 UNICAST PKTS SENT:               7  LS ADV. AGED OUT:                 1 
 LS ADV. FLUSHED:                 1  PTRS TO INVALID LS ADV:           0 



  • LSTYPE=2 is “Network links the set of routers attached to a network”.
  • is an LS destination (from F OMP1,ospf,database,areaid=…) It comes from the frr definition below
interface eno1
   ip address peer

Only addresses on the Server are accepted. Addresses from the Laptop are not valid.

In the command F OMP1,OSPF,LSA,LSTYPE=1,LSID=, some of the LINK IDs seem to be valid.


This allows you to see a lot of information about an individual element of the OSPF database.

The LSATYPE is described in here. LSTYPE=1 is for Router Links Advertisment.

The LSID is one of the routers, for example in

  • F OMP1,ospf,database,areaid=, it displays, LS DESTINATION LS ORIGINATOR
  • F OMP1,ospf,neighbor, it displays NEIGHBOR ID
  LS DESTINATION (ID):                     
  ROUTER TYPE:      (0X00)                         
  # ROUTER IFCS:   3                               
     LINK ID:               
     LINK DATA:               
        INTERFACE TYPE:   2
     LINK ID:
     LINK DATA:              
        INTERFACE TYPE:   2 
     LINK ID:              
     LINK DATA:              
        INTERFACE TYPE:   2 


 TYPE   DEST NET         MASK      COST    AGE     NEXT HOP(S) 
 STAT*         FF000000  0       16079 
  SPF         FFFFFF00  101     16071         (2) 
  SPF*         FFFFFF00  1       16078   ETH1 
  SPF*         FFFFFF00  1       16078   JFPORTCP4 
  SPF         FFFFFFFF  201     4733         (2) 
                        0 NETS DELETED, 3 NETS INACTIVE 

(2) is the number of equal-cost routes to the destination.



EZZ7874I ROUTE EXPANSION 105                   
ROUTE TYPE:     SPF                            
DISTANCE:       101                            
AGE:            943                            
NEXT HOP(S):          (ETH1)       

Authenticating ospf

This is another of those little tasks that look simple but turn out to be more a little more complex than it first looked.

Authentication in OSPF is performed by sending authentication data in every flow. This can be a password (not very secure) or an MD5 check sum, based on a shared password and sequence number. The receiver checks the data sent is valid, and matches the data it has.

Enabling authentication on Linux

To do any authentication you need to enable it at the area level.

router ospf
  ospf router-id
  area authentication

This turns it on for all interfaces – defaulting to password based with a null password. I did this and my connections failed because the two ends of the link were configured differently.

I first had to configure ip ospf authentication null for all interfaces, then enable area authenticate, and the the connections to other systems worked.

interface tap2
   ip ospf area
   ip ospf authentication null

interface ...

router ospf
  ospf router-id
  area authentication

I could then enable the authentication on an interface by interface basis.

If there is a mismatch,

  • z/OS will report a mismatch,
  • frr quietly drops the packet. I enabled packet trace.

debug ospf packet hello

I got out a trace

OSPF: ... interface enp0s31f6: auth-type mismatch, local Null, rcvd Simple
OSPF: ... ospf_read[]: Header check failed, dropping.

The router ospf … area … authentication is the master switch.

To define authentication on a link, you have to change both ends, then activate the change at the same time at each end.

On z/OS

I could not find how to get OMPROUTE to reread its configuration file after I updated and OSPF entry. There is an option

f OMP1,reconfig

but the documentation says

Reread the OMPROUTE configuration file. This command ignores all statements in the configuration file except new OSPF_Interface, RIP_Interface, Interface, IPv6_RIP_Interface, and IPv6_Interface

and I got messages like

EZZ7821I Ignoring duplicate OSPF_Interface statement for

For z/OS OMPROUTE to communicate with frr (and CISCO routers) I had to specify the z/OS definition Authentication_… for example

ospf_interface IP_address= 

Then stop and restart OMPROUTE.

Using password (or not)

If you use a password, then it flows in clear text. Anyone sniffing your network will see it. It should not be used to protect your system.

On frr

You need router ospf area … authentication. If you have area … authentication message-digest then the password authentication statement on the interface is ignored.

router ospf
  ospf router-id
  router-info area
  area authentication

interface tap0
   ip ospf authentication colin

On z/OS

ospf_interface IP_address= 

Using MD5


An MD5 checksum is calculated from

  • the key – a string of up to 16 bytes
  • key id – an integer in the range 0-255. In the future this key could be used to specify which checksum algorithm to use. Currently only its value is used only as part of the check sum calculation.
  • the increasing sequence number of the flow.

This checksum is calculated and the sequence number and checksum are sent as part of each flow. The remote end performs the same calculation, with the same data, and the checksum value should match.

Because the sequence number changes with every flow, the checksum value changes with every flow. This prevents replay attacks.

The key must be the same on both ends of the connection. Because frr and hardware routers are based in ASCII, an ASCII value must be specified when using z/OS and these routers.

On frr

router ospf
  ospf router-id
  area authentication 

interface tap0
   ip ospf authentication message-digest
   ip ospf message-digest-key 3 md5 AAAAAAAAAAAAAAAA

On z/OS

ospf_interface IP_address= 
     ;     Authentication_Key=A"AAAAAAAAAAAAAAAA" 

You can either specify the ASCII value A”A…” or as hex “0x4141…” where 0x41 is the value of A in ASCII.

The z/OS documentation is not very clear. My edited version is

The value of the authentication key for this interface. This value must be the same for all routers attached to a common medium a link. The coding of this parameter depends on the authentication type being used on this interface.

For authentication type MD5, code the 16-byte authentication key used in the md5 processing for OSPF routers attached to this interface.

This value must be the same at each end.

If the router at the remote end is ASCII based, for example CISCO or Extreme routers, or the frr package on Linux, this value must be specified in ASCII.

You can specify a value in ASCII as A”ABCD…” or as hexadecimal 0x41424344…”, were 41424344 is the ASCII for ABCD.

For non ASCII routers you can specify an ASCII or hexadecimal value.   You can use pwtokey to generate a suitable hexadecimal key from a password.

What does tso netstat neighbour give you?

The command TSO NETSTAT ND gave me

Query Neighbor cache for 2001:db8:1:0:8024:bff:fe45:840c 
  IntfName: IFPORTCP6          IntfType: IPAQENET6 
  LinkLayerAddr: 82240B45840C  State: Reachable 
  Type: Router                 AdvDfltRtr: No 

Query Neighbor cache for fe80::8024:bff:fe45:840c 
  IntfName: IFPORTCP6          IntfType: IPAQENET6 
  LinkLayerAddr: 82240B45840C  State: Reachable 
  Type: Router                 AdvDfltRtr: No 

Query Neighbor cache for fe80::9863:1eff:fe13:1408 
  IntfName: JFPORTCP6          IntfType: IPAQENET6 
  LinkLayerAddr: 9A631E131408  State: Reachable 
  Type: Router                 AdvDfltRtr: No 

On Linux the

ip -6 addr

command gave me

tap1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UNKNOWN qlen 1000
    inet6 2001:db8:1:0:b0fd:f92b:8362:577b/64 ...
    inet6 2001:db8:1:0:8024:bff:fe45:840c/64 ...
    inet6 fe80::8024:bff:fe45:840c/64 ...

tap2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UNKNOWN qlen 1000
    inet6 fe80::9863:1eff:fe13:1408/64 ...

The TSO output means

  • Query Neighbor cache for 2001:db8:1:0:8024:bff:fe45:840c. The address is one of the addresses on the remote end of the connection. There is an entry because some traffic came via the address.
  • IntfName: IFPORTCP6 The z/OS Interface name used to create the defintion
  • IntfType: IPAQENET6 the OSA-Express QDIO interfaces statement
  • LinkLayerAddr: 82240B45840C
  • State: Reachable Other options can include stale, which means z/OS has not heard anything from this address for a while
  • Type: Router
  • AdvDfltRtr: No. The information passed in the Router Advertisement, said this was connection does not Advertise a Default Router(AdvDfltRtr).

From the NETSTAT ND output we can see data has been received from

  • IFPORTCP6:2001:db8:1:0:8024:bff:fe45:840c
  • IFPORTCP6:fe80::8024:bff:fe45:840c
  • JFPORTCP6:fe80::9863:1eff:fe13:1408

To get data to flow down the 2001…. address I had to use

ping -I 2001:db8:1:0:8024:bff:fe45:840c 2001:db8:1::9

Where the -I says use the interface address.

You can get information about bytes processed by interface (not by address) using the TSO NETSTAT DEVLINKS command.

Getting IP v6 static routing from Linux to/from z/OS

For me this was an epic journey, taking weeks to get working. It was like a magical combination lock, which will not open unless all of the parameters are correct, today has an ‘r’ in the month, and you are standing on one leg. Once you know the secrets, it is easy.

With IP V6 there is a technology called dynamic discovery which is meant to make configuring your IP network much easier. Each node asks the adjacent nodes what IP addresses they have, and so your connection to the next box magically works. I could not get this to work, and thought I would do the simpler task of static configuration – this had similar problems – but they were smaller problems.

There were two three four five six seven key things that were needed to get ping to work in my setup:

The key things

Allow forwarding between interfaces

On Linux

sudo sysctl -w net.ipv6.conf.all.forwarding=1

The documentation says “… conf/all/forwarding – Enable global IPv6 forwarding between all interfaces”.

Clearing the cache

Routing and neighbourhood definitions are cached for a period. If you change a definition, and activate it, an old definition may still be used. I found I got different results if I rebooted, re-ipled, or went for a cup of tea; it worked – then next time I tried it with the same definitions, it did not work. Clearing the routing and neighbourhood cache made it more consistent.


On Linux use sudo ip -6 neigh flush all

Put a delay between creating definitions and using them.

I had a 2 second delay between creating a definition, and using it, which helped getting it to work. I think data is propagated between the system, and issuing a ping or other command immediately after a definition, was too fast for it,

A timing window

I had scripts to clear and redefine the definitions. Some times if I ran the laptop script then the server script, then ping would not work. If I reran the laptop script, then usually ping worked. Sometimes I had to rerun the server script.

The default route would often change.

The wireless connection to the server was unreliable. There would be a route from my laptop to the server via the wireless. Then a few minutes later the connection to the server would stop, and so alternate routes had to be used, because traffic via the wireless would be dropped.

I got around this problem, by explicit coding of the routes and not needing to use the default definitions. (Also disabled the wireless connection while debugging)

The correct route syntax

I found I was getting “Neigbor Solicitation” instead of the static routing. To prevent this the route on the laptop needed the via…

sudo ip -6 route add 2001:db8:1::9/128 via 2001:db8::2 dev enp0s31f6

and not

sudo ip -6 route add 2001:db8:1::9/128                dev enp0s31f6

See Is “via” needed when creating a Linux IP route?

The z/OS IP address kept changing across IPLs

Why is my z/OS IP address changing when using zPDT, and routing does not work?


  • The laptop had an Ethernet connection to the server.
  • The server had an Ethernet like connection to z/OS. This was a tunnel(tap1), looking like an OSA to z/OS

The addresses:

Laptop Ethernet (enp0s31f6)2001:db8:::7
Server Ethernet (eno1)2001:db8:::2
Server Tunnel (tap1)2001:db8:1::3
Z/OS interface (ifacecp6)2001:db1::9

The Laptop side had prefix 2001:db8:0::/64, the z/OS side had prefix 2001:db8:1::/64 . See One minute topic: Understanding IP V6 addressing and routing if these numbers look strange.


z/OS routing definitions

;     Destination      FirstHop          LinkName   Size 
ROUTE default6         2001:db8:99::3    IF2        MTU  1492
ROUTE 2001:db8:99::/64 2001:db8:99::3    IF2        MTU 5000 

ROUTE 2001:db8::/64    2001:db8:1::3     IFPORTCP6  MTU 5000 
ROUTE 2001:db8:1::/64  2001:db8:1::3     IFPORTCP6  MTU 5000 


  • default6 says if no other routes match, then send the traffic down IF2 connection. At the remote end of the IF2 connection, it has IP address 2001:db8:99::3.
  • Traffic for 2001:db8:99::/64 should be sent down interface IF2 – which has an address 2001:db8:99::3 at the remote end
  • Traffic for 2001:db8::/64 (2001:db8:0::/64) should be sent down interface IFPORTCP6 which has address 2001:db8:1::3 at the remote end.
  • Traffic for 2001:db8:1::/64 should be sent down interface IFPORTCP6 which has address 2001:db8:1::3 at the remote end.

I needed a route for both 2001:db8::/64 and 2001:db8:1::/64 as one was the route to the laptop, the other was the route to the Linux server.

Linux Server machine

On my Linux machine I had

from ip -6 addr

tap1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UNKNOWN qlen 1000
 inet6 2001:db8:1::3/64 scope global 
    valid_lft forever preferred_lft forever
 inet6 2001:db8::3/64 scope global 
    valid_lft forever preferred_lft forever
 inet6 fe80::e852:31ff:fe0f:81da/64 scope link 
    valid_lft forever preferred_lft forever

I used the global address 2001:db8:1::3 in my z/OS routing statement.

The documentation implies I should use the link-local address fe80::e852:31ff:fe0f:81da in my static z/OS definitions, but I could not see how to use this, as it changed every time I ipled my z/OS. This means I need to explicitly define an address on Linux for this connection ( 2001:db8:1::3).

Linux Server definitions

On my Linux server I defined static definitions.

sudo sysctl -w net.ipv6.conf.all.forwarding=1

# clear the state every time
sudo ip -6 route flush root 2001:db8:1::/64
sudo ip -6 route flush root 2001:db8::/64
sudo ip -6 neigh flush all 

# define the interface to z/OS
sudo ip -6 addr del 2001:db8:1::3/64 dev tap1
sudo ip -6 addr add 2001:db8:1::3/64 dev tap1

sudo ip -6 addr del 2001:db8::2/64 dev eno1
sudo ip -6 addr add 2001:db8::2/64 dev eno1

sudo ip -6 route del 2001:db8::/64 dev eno1
sudo ip -6 route add 2001:db8::/64 dev eno1

sudo ip -6 route del 2001:db8:1::9 dev tap1
sudo ip -6 route add  2001:db8:1::/64   dev tap1

# sudo traceroute -d -m 2 -n -q 1 -I    2001:db8::7 
# ping 2001:db8::7 -c 1 -r
# ping 2001:db8:1::9 -c 1 -r

This script grew as I added all of the options to get it to work.

The statements are

sudo sysctl -w net.ipv6.conf.all.forwarding=1

This enables the cross interface traffic.

sudo ip -6 route flush root 2001:db8:1::/64
sudo ip -6 route flush root 2001:db8::/64
sudo ip -6 neigh flush all

These clear the routing for the two addresses, and for the neighbourhood cache. I do not know if these are required, without them the results were not consistent.

#give the interface to z/OS an explicit address
sudo ip -6 addr del 2001:db8:1::3/64 dev tap1
sudo ip -6 addr add 2001:db8:1::3/64 dev tap1

#give the connection to the Laptop an explicit address
sudo ip -6 addr del 2001:db8::2/64 dev eno1
sudo ip -6 addr add 2001:db8::2/64 dev eno1

These deleted then created global addresses for the server end of the interfaces.

sudo ip -6 route del 2001:db8::/64 dev eno1
sudo ip -6 route add 2001:db8::/64 dev eno1

sudo ip -6 route del 2001:db8:1:: dev tap1
sudo ip -6 route add 2001:db8:1:: dev tap1

These deleted and created routes the traffic to the interfaces. I could have used route rep…

Linux Laptop definitions

#Give the ethernet connection to the server an explicit address
sudo ip -6 addr add 2001:db8::19 dev enp0s31f6

#create the route to the server using the via
sudo ip -6 route del 2001:db8:1::/64 dev enp0s31f6
sudo ip -6 route add 2001:db8:1::/64 via 2001:db8::2 dev enp0s31f6

I needed to specify

  • an explicit to the address of the interface to the server, so it could be used as a destination from z/OS.
  • the route to get to the server. I needed to specify the via, so the static route was used directly. Without the via, it tried to use Neighbourhood discovery.


For “ping” to work, the packet has to reach the destination and the reply get back to the originator. See Understanding ping and why it does not answer.

If I pinged 2001:db8:1::9 (z/OS) from the Linux server (the end of the IFPORTCP6 connection) the traffic came from address 2001:db8:1::3, The reply was sent back using the matching 2001:db8:1::/64 definitions.

If I pinged 2001:db8:1::9 (z/OS) from my laptop, through the Linux server to z/OS, the traffic came from address 2001:db8::7. The reply was sent back using the matching 2001:db8::/64 definitions.

If I pinged 2001:db8::7 (laptop) from z/OS it was sent back using the matching 2001:db8::/64 definitions.

Understanding radvd with IPV6 on Linux.

My two day project to deploy IP V6 dynamic routing, turned into an eight week project before I got it to work.

I am documenting a lot of what I learned – today’s experience is understanding what radvd is and what the configuration options mean. I found a lot of documentation – most of which either assumed you know a lot, or only provided an incomplete description.

High level view of what radvd provides

There are several ways of providing configuration to TCPIP. One way is using radvd (on Linux).

In a configuration file you give

  • An interface name
    • Which IP addresses (and address ranges) are available at the remote end of the connection.
    • Which IP addresses (and address ranges) are available at the local end of the connection

From the information about the local end, the remote end can build its routing tables.

Background IP routing

With IP you can have

  • static routing, where you explicitly give the routes to a destination – such as to get to a.b.c.d – go via xyz interface. You have to do a lot of administration defining the addresses of each end of an interface (think Ethernet cable)
  • dynamic routing, and neighbourhood discovery, where the system automatically finds the neighbours and there is less work for an administrator to do.

With IPv6 you have

  • global addresses with IP addresses like 2001:db8:1:16…..
  • link-local addresses. These are specific to an interface. An Ethernet connection can have many terminals hanging off ‘the bus’. The link-local address is only used within the connection. A different Ethernet cable can use the same address. There is no problem as the addresses are only used with the cable.
  • Neighbour Discovery. Rather than specify every thing as you do with static routing, IP V6 supports Neighbour Discovery, where each node can tell connected nodes, what routes and IP addresses it knows about. This is documented in the specification. This supports
    • Router Advertisement (RA), (“Hello, I’m a router, I know about the following addresses and routes”),
    • Router Solicitation (RS), (“Hello, I’ve just started up, are there any routers out there?”),
    • Neighbour Solicitation(NS) (“Does anyone have this IP address?”), and
    • Neighbour Advertisement (Usually in response to a Neighbour Solicitation, “I have this address”).

What is radvd?

The radvd program is a Router Advertisment Daemon (RADvd) which provides fakes router information – but is not a router.

You specify a configuration file. The syntax is defined here.

You can specify that this interface provides a “default” route. See here.

Example definition

I have a Linux Server, and a laptop running Linux connected by an Ethernet cable.

For the server, the radvd.conf file has

# define the ethernet connection
interface  eno1
   AdvSendAdvert on; 
   MaxRtrAdvInterval 60;
   MinDelayBetweenRAs  60; 
   prefix 2001:ccc::/64 
   #     AdvOnLink on;
   #     AdvAutonomous on;
     AdvRouterAddr on; 
   route 2001:ff99::/64
   #   AdvRoutePreference medium;
   # 3600 = 1 hour
      AdvRouteLifetime 3600;

The key information is


Data following #

The name of the interface

interface eno1{….};

prefix statement

prefix 2001:ccc::/64{…}

2001:ccc::/64 is the ipv6 address range or, to say it another way, ipv6 addresses with the left 64 bits beginning with 2001:0ccc:0000:0000. In IP V6 this is known as the prefix.

Basically this prefix statement means “this interface is a route to the specified prefix”.

This creates some addresses on the server for the connection.

eno1    inet6 2001:ccc::e02a:943b:3642:1d73/64 scope global temporary dynamic...       
eno1    inet6 2001:ccc::dbf:5c90:61a6:20ae/64 scope global dynamic mngtmpaddr...
eno1    inet6 2001:ccc::c48b:e8f1:495c:5b52/64 scope global temporary dynamic ...       
eno1    inet6 2001:ccc::2d8:61ff:fee9:312a/64 scope global dynamic mngtmpaddr ...

create routes

The prefix statement creates a route on the server to get to the laptop

2001:ccc::/64 dev eno1 proto ra metric 100 pref medium
2001:ccc::/64 dev eno1 proto kernel metric 256 ...

This says that on the server, if there is a request for an address in the range 2001:ccc::/64 send it via device eno1.

route 2001:ff99::/64 statement.

This passes information to the remote end of the connection, see below. It says “I (the server) know how to route to 2001:ff99::/64”.

It the routing address does not show up in any ip -6 commands on the server.


The radvd code periodically sends information along the connection to the other end, at an interval you specify. See radvdump below on how to display it.

At the other end of the connection…

At the remote (laptop) end of the connection, using WiresShark to display the data received, shows a Router Advertisement with

Internet Protocol Version 6, Src: fe80::a2f0:9936:ddfd:95fa, Dst: ff02::1
Internet Control Message Protocol v6
    Type: Router Advertisement (134)
    ICMPv6 Option (Prefix information : 2001:ccc::/64)
    ICMPv6 Option (Route Information : Medium 2001:ff99::/64)
    ICMPv6 Option (Source link-layer address : 00:d8:61:e9:31:2a)


  • fe80::a2f0:9936:ddfd:95fa is the link-local address on the server machine
  • ff02::1 the multicast address “All nodes” on a link (link-local scope)”
  • Prefix information : 2001:ccc::7/64 the prefix of the IP address 2001:ccc:0:0…
  • Route Information : Medium 2001:ff99::/64 This is from the “route” in the radvd configuration file on the Linux Server. It tells the laptop that this connection knows about routing to 2001:ccc::/64 .

From the route information it dynamically creates a route on the laptop to the server.

2001:ff99::/64 via fe80::a2f0:9936:ddfd:95fa dev enp0s31f6 proto ra metric 100 ...

This creates a route to 2001:ff99::/64 via the IP address fe80::….95fa, from the laptop end of the Ethernet connection with name enp0s31f6 to where-ever the connection goes to (in this example it goes to my server).

If I ping 2001:ffcc::9 from the laptop, it will use this route on its way to the z/OS server.

Connection to z/OS

Within the radvd.conf file is the definition to get to z/OS. This interface looks like an Ethernet (the ip -6 link command gives link/ether). This is for a different radvd configuration file to the earlier example.

interface  tap1
   AdvSendAdvert on; 
   MaxRtrAdvInterval 60;
   MinDelayBetweenRAs  60; 
   AdvManagedFlag  on;
   AdvOtherConfigFlag on;
   prefix 2001:db8:1::/64
     AdvOnLink on;
     AdvAutonomous on;
     AdvRouterAddr on;
   prefix 2001:db8:1::99/128
     AdvOnLink on;
     AdvAutonomous on;
     AdvRouterAddr on;

   route 2001:db8::/64
     AdvRoutePreference medium;
     AdvRouteLifetime 3100;

This says there are IP addresses in the range 2001:db8:1::/64 via this connection. z/OS reads the Router Advertisement and creates a route for them. TSO Netstat route gives

DestIP:   2001:db8:1::/64 
  Gw:     :: 
  Intf:   IFPORTCP6         Refcnt:  0000000000 
  Flgs:   UD                MTU:     9000 

The explicit IP address, with the 128 to specify use the whole value, rather than just the prefix,

 prefix 2001:db8:1::99/128
     AdvOnLink on;
     AdvAutonomous on;
     AdvRouterAddr on;    

creates a route in z/OS; from TSO NETSTAT ROUTE

DestIP:   2001:db8:1::99/128 
  Gw:     :: 
  Intf:   IFPORTCP6         Refcnt:  0000000000 
  Flgs:   UHD               MTU:     9000 

In UHD, the U says the interface is Up, the H says this is for a host (a specific end point), and the D says this is dynamically created.

If you try to ping 2001:db8:1::99 from the server, a Neighbour Solicitation request is sent from the server to z/OS, asking “do you have 2001:db8:1:99?”. My z/OS did not have that defined and so did not respond.

When I defined this address on z/OS TCPIP using the obeyfile

    INTFID 7:7:7:7 
    ADDADDR 2001:DB8:1::9 
    ADDADDR 2001:DB8:9::9 
    ADDADDR 2001:DB8:1::99 

(And used

  • v tcpip,,sto,ifportcp6
  • v tcpip,,obeyfile,USER.Z24C.TCPPARMS(IFACE61)
  • v tcpip,,sta,ifportcp6

to activate it)

After this, the ping was successful because there was a neighbour solicitation for 2001:db8:1::99, and z/OS replied with Neighbour Advertisement of 2001:db8:1::9 saying I have it.

Create a default route

If you specify AdvDefaultLifetime 0 on the interface, this indicates that the router is not a default router and should not appear on the default router list in the Router Advertiser broadcasts. If the value is non zero, the recipient, can use this connection as a default route, for example there is no existing default route. A statically defined default will be used in preference to a dynamically defined one.

Use radvdump to display what it sent in the RA

You can use sudo radvdump to display what is being sent in the Router Advertiser message broadcast over multicast. It looks just like the radvd.conf file.