One minute networking: getting your data to flow around the corner; IP tunnelling

This is another of the little bits of networking knowledge, which, once you understand it, is obvious! Some of the documentation on the web is either wrong or is missing information.

The original problem

I wanted to use a route management protocol (OSPF) for managing the routing information known by each router. It has its own format packets. Not every device or router supports these packets.

You configure the interface name, and the OSPF data flows through the interface.

When the connection is a direct line, the data is passed to the remote system and it can use it. When the connection is indirect, for example via a wireless router. The wireless router does not know how to handle the OSPF packets and throws them away. The result is that my remote machine does not get the OSPF packets.

The solution – use a tunnel

One solution is to wrap the packets of data, so they get passed up to the router, round the corner, and back down to the remote system.

When I was employed, we had an internal mail system for paper correspondence . If we wanted to send a letter to a different site, we took the piece of internal mail, put it in an envelope and sent it through the national mail to the remote site. At the remote site, the mail room removed the external envelope, and sent the internal letter on to the recipient. It is a similar process with IP tunnelling.

I have a laptop with IP address A.B.C.D and a server with address W.X.Y.Z., I can ping from A.B.C.D to W.X.Y.Z, so there is an existing path between the machines.

You define a tunnel to W.X.Y.Z (the external envelope) and give which interface address on your system it should use. (Think of having two mail boxes for your letter, one for Royal Mail, another for FedEx).

You define a route so as to say to get to address p.q.r.s use tunnel ….

The definitions

The wireless interface for my laptop was 192.168.1.222 . The wireless address of my server was 192.168.1.230

I defined a tunnel from Laptop to Server called LS

sudo ip tunnel add LS mode gre local 192.168.1.222 remote 192.168.1.230

Make it active and define the address on the server 192.168.3.3 .

sudo ip link set LS  up
sudo ip route add 192.168.3.3 dev LS

If I ping 192.168.3.3 the enveloped packet goes to the server machine 192.168.1.230 . If this address is defined on the server the ping sends a response – and the ping worked!

Except it didn’t quite. The packet got there, but the response did not get back to my laptop.

At the server the ping “from” IP address was 10.1.0.2, attached to my laptop’s Ethernet. This was not known on the server.

I had three choices

  • Define a tunnel back from the server to the laptop.
  • Use ping -I 192.168.1.222 192.168.3.3 which says send the ping request to 192.168.1.1 , and set the originator address to 192.168.1.222. The server knows how to route to this address.
  • Define a route from the server back to my laptop.

The simplest option was to use ping -I … because no additional definitions are required.

This does not solve my problem

To get OSPF data from the server to my laptop, I need a tunnel from the server to my laptop; so a tunnel each way

Different sorts of data are used in an IP network

  • IPV6 and IPV4 – different network addressing schemes
  • unicast and multi cast.
    • Unicast – Have one destination address, for example ping, or ftp
    • Multicast – Often used by routers and switches. A router can send a multicast broadcast to all nodes on the local network for example ‘does any nodes have IP address a.b.c.d?‘. The data is cast to multiple nodes.

When I defined the tunnel above I initially specified mode ipip. There are different types of tunnel mode ipip is just one. The list includes

  • ipip – Virtual tunnel interface IPv4 over IPv4 can send unicast traffic, not multi cast
  • sit – Virtual tunnel interface IPv6 over IPv4.
  • ip6tnl – Virtual tunnel interface IPv4 or IPv6 over IPv6.
  • gre – Virtual tunnel interface GRE over IPv4. This supports IPv6 and IPv4, unicast and multicast.
  • ip6gre – Virtual tunnel interface GRE over IPv6. This supports IPv6 and IPv4, unicast and multicast.

The mode ipip did not work for the OSPF data.

I guess that the best protocol is gre.

Setting up a gre tunnel

You may need to load the gre functionality

sudo modprobe ip_gred
lsmod | grep gre

create your tunnel

sudo ip tunnel add GRE mode grep local 192.168.1.222 remote 192.168.1.230 
sudo ip link set GRE  up
sudo ip route add 192.168.3.3 dev GRE

and you will a matching definition with the same mode at the remote end.

Displaying the tunnel

The command

ip link show dev AB

gives information like

9: AB@NONE: mtu 1476 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000 link/gre 192.168.1.222 peer 192.168.1.230

where

  • link/gre this was defined using mode gre
  • 192.168.1.222 the local interface to be used to send the traffic
  • peer 192.168.1.230 the IP address for the far end

The command

ip route

gave me

192.168.3.3 dev AB scope link

so we can see it gets routed over link(tunnel AB).

Using the tunnel

I could use the tunnel name in my defintions, for example for OSPF

interface AB
   area 0.0.0.0

How to reduce the chance of screwing up in a Linux window.

I had multiple Linux terminal windows open, doing SSH to different machines. I typed shutdown in the wrong window – and the wrong server shutdown!

I had configured different profiles so I could have a white background, a green background and a yellow background for my different systems, but I had got careless and not used them.

I found a neat way of colouring the windows automatically.

xdotool is a command-line X11 automation tool, which allows you to programmatically press keys. You can use this to set the profile of a terminal window.

To create a profile

From the hamburger options,

  • preferences,
  • profiles +
  • give the profile a name, create
  • select the named profile, it will display customising options
  • colours
  • untick Use colours from system theme
  • Click Text or Background
  • Pick a colour, Select
  • Close the window

Select a profile

Manually

  1. From the hamburger option
    • Select Profile
    • Pick a profile
  2. or Shift+f10
    • r (for Profile)
    • 3 for the third option in the list

Programmatically

xdotool key shift+F10 r 3

This does Shift+10, then select r for Profile, then picks the 3rd option

The clever bit

You can make an alias such as

alias somehost="xdotool key shift+F10 r 3; ssh user@somehost; xdotool key shift+F10 r 2"

or a somehost.sh script

#!/bin/sh
xdotool key shift+F10 r 3
ssh me@10.1.0.5
xdotool key shift+F10 r 2

If you enter the somehost command – it will select the 3rd profile, do the ssh. On exit from ssh it resets it back to the 2nd profile.

Restore files from Linux using Duplicity

Duplicity is a program which manages backup and restore of files on your Linux machine.

What is duplicity?

Duplicity backs directories by producing encrypted tar-format volumes and uploading them to a remote or local file server. Because duplicity uses librsync, the incremental archives are space efficient and only record the parts of files that have changed since the last backup. Because duplicity uses GnuPG to encrypt and/or sign these archives, they will be safe from spying and/or modification by the server.

Backing up files

You run the backup application, and can specify the directories to backup. You can specify which directories to ignore.

The backups can be stored

  • Google drive
  • Networks server
  • Locally attached drive
  • Local Folder

That’s the easy bit.

What files are backed up?

I have my backups going to an external USB drive /media/colinpaice/UbuntuBackup1/home/Backup2024 on my Linux machine. The files have names like

duplicity-full.20240308T084825Z.vol295.difftar.gpg

The command

duplicity list-current-files file:///media/colinpaice/UbuntuBackup1/home/Backup2024 >files2024

Restore a file

duplicity restore -t 3D –file-to-restore ~/ssl/ssl2/rsaca256.csr file:///media/colinpaice/UbuntuBackup/home/Backup2021 ~/ssl/ssl2/rsa256.csr

This restores a file

  • -t 3D from 3 days ago
  • –file-to-restore ~/ssl/ssl2/rsaca256.csr
  • file:///media/colinpaice/UbuntuBackup/home/Backup2021 from this device
  • ~/ssl/ssl2/rsa256.csr to this file

What next

Duplicity can do much more than this. Ive just provided information on the most basic stuff that I have used. See the products web page or man duplicity

IPV6 getting an address automagically

You can use static definitions to give a device or link an IP address. You can use modern(last 20 years) technology to do this for you – and get additional advantages.

A server application needs a fixed IP address and port. A client, connecting to the server, can use a different IP address and port on different days. This has the advantage that it makes it harder for the bad guys to track you from your address and port combination

Client application usually use the option “allocate me any free port”.

To get a different IP address every time you can use IPv6 Stateless Address Auto-configuration (SLAAC). It is called stateless because it does not need to remember any state information from one day to the next. The client application says “give me an IP address, any IP Address” and then uses the IP address, until the device is shutdown, or the interface is closed.

On Linux You need radvd for this to work.

Router Advertisement Daemon (radvd)

You used to have dedicated routers. Now you can run radvd on a computer and it acts like a router. You can run it on your personal machine, or run it in its own machine.

This supports Neighbor Discovery Protocol. When your machine connects to the network, it asks all routers on your local network for configuration information. It gets back a list of prefixes defined on the router (for example 2001:db8::/64). If your machine wants to send a packet to 2001:db8::99, it sends a request to all routers on the local network, asking if any router has 2001:db8::99 defined. If so, the router responds, and so your machine knows where to send the packet to.

When an IP address is allocated to a device, it sends a request to all devices in the local network, asking “does anyone have this address”. This avoids devices with the same IP address. It is known as Duplicate Address Detection (DAD).

My radvd config file

The syntax of the configuration file is defined here

For my interface vl100 I wanted it to give it an IP address 2100… and 2100…

interface  vl100
{
   AdvSendAdvert on; 
   MaxRtrAdvInterval 60;
   MinDelayBetweenRAs  3; 
   
   prefix 2100::/64
   {
     AdvAutonomous on;
   };
    prefix 2200::/64
   {
   };
};

Where

  • AdvAutonomous on (the default) says support SLAAC

Creates

: vl100@enp0s31f6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 2200::3905:281e:909b:5e00/64 scope global temporary dynamic 
       valid_lft 86398sec preferred_lft 14398sec
    inet6 2200::8e16:45ff:fe36:f48a/64 scope global dynamic mngtmpaddr 
       valid_lft 86398sec preferred_lft 14398sec
    inet6 2100::3863:da22:619a:42e0/64 scope global temporary dynamic 
       valid_lft 86398sec preferred_lft 14398sec
    inet6 2100::8e16:45ff:fe36:f48a/64 scope global dynamic mngtmpaddr 
       valid_lft 86398sec preferred_lft 14398sec
    inet6 fe80::8e16:45ff:fe36:f48a/64 scope link 
       valid_lft forever preferred_lft forever

See here for the meaning of the fields

The attributes of the connection include :scope global temporary dynamic

  • dynamic was created by using stateless SLAAC configuration. If the address was created by an ip -6 addr add … dev … command, it will not have dynamic.
  • tentative – in the process of Duplicate Address Detection processing.
  • temporary – it expires after the time interval.
  • mngtmpaddr – is used as a template for temporary connections

You can change the attributes of an address using the change command. For example to change the time out value

sudo ip -6 addr change 2200::… dev vl100 valid_lft 100 preferred_lft 10

For me it expired and generated another connection with the same address.

One minute mvs: catalogs and datasets.

In days of old, when 64KB was a lot of real storage, to reference a data set you had to specify the data set name and the DASD volume the data set was on. DSN=MY.JCL,VOL=SER=USER00

After this, the idea of a catalog was developed. Just like the catalog in a library, it told you where things were stored. When you created a data set, and specified DISP=(NEW,CATLG), the data set name and volume were stored in the catalog. When you wanted to use a data set, and did not specify the volume, then the catalog was used to find the volume for the data set.

As systems grew and the number of data sets grew, the catalog grew and quickly became difficult to manage. For example if you deleted data sets, the entry was logically removed from the catalog, resulting in gaps in the catalog.

After this a multi level catalog was developed. You have one master catalog. You can have many user catalogs. You define an alias in the master catalog saying for data sets starting with a specific high level qualifier, use that user catalog.

When a userid was created, most system programmers would also create an alias pointing to a user catalog. They may define a user catalog for each user, or a user catalog could be shared by many aliases.

The catalogs are managed by the VSAM component of z/OS.

Entity naming

PDS and sequential files are referred to as datasets. VSAM provides simple database objects,

  • Relative Record ( where you say get me the n’th record)
  • Key sequence. You define a primary index, and you can an index on different columns using an ALTERNATIVE INDEX. 

VSAM uses the term cluster to what you use in you JCL or application. A cluster has a data component, and zero or more index components.

Moving systems.

I have been running on a self contained ADCD system at z/OS level 2.4. I have recently installed a self contained system at z/OS 2.5. How do I get my data sets into the new system?
You can import connect a user catalog into a new (master) catalog, and define an alias in the new master catalog pointing to the user catalog.

When I did this I could then see my COLIN.* data sets. To be able to use the data sets, I need the volumes to be attached to the z/OS system.

Useful IDCAMS commands

In batch you use the IDCAMS program (IDC = prefix for VSAM, AMS is for Access Management Services!)

If you do not specify a catalog, it defaults to the master catalog.

Create a user catalog

//IBMDF  JOB 1,MSGCLASS=H                                   
//S1  EXEC PGM=IDCAMS                                       
//SYSPRINT DD SYSOUT=*                                      
//SYSIN DD *                                                
 DEFINE USERCATALOG -                                       
      ( NAME('A4USR1.ICFCAT') -                             
        MEGABYTES(15 15) -                                  
        VOLUME(A4USR1) -                                    
        ICFCATALOG  -                                       
        FREESPACE(10 10) -                                  
        STRNO(3  ) ) -                                      
        DATA( CONTROLINTERVALSIZE(4096) -                   
              BUFND(4) ) -                                  
        INDEX(BUFNI(4) )                                    
/*

List an entry

You can list information about an entry, such as a data set, or a catalog using the LISTCAT command

LISTCAT ENT(COLIN.USERS) ALL

Listing aliases

You can use the IDCAMS command LISTCAT with alias

LISTCAT ALIAS

which gives a one line per entry list of all of the aliases

ALIAS --------- ADCDA       
ALIAS --------- ADCDB       
ALIAS --------- ADCDC       
ALIAS --------- ADCDD       
...

LISTCAT ALIAS ALL

gives 

ALIAS --------- ADCDA                                                       
     ...          
     ENCRYPTIONDATA                                                         
       DATA SET ENCRYPTION-----(NO)                                         
     ASSOCIATIONS                                                           
       USERCAT--USERCAT.Z24C.USER                                           
ALIAS --------- ADCDB                                                       
    ...      
     ENCRYPTIONDATA                                                         
       DATA SET ENCRYPTION-----(NO)                                         
     ASSOCIATIONS
       USERCAT--USERCAT.Z24C.USER

So we can see that the the alias ADCDA maps to user catalog USERCAT.Z24C.USER

Listing a catalog

The command

LISTCAT CATALOG(USERCAT.Z24C.USER)

gives

CLUSTER ------- 00000000000000000000000000000000000000000000       
   DATA ------- USERCAT.Z24C.USER                                  
   INDEX ------ USERCAT.Z24C.USER.CATINDEX                         
NONVSAM ------- ADCDA.S0W1.ISPF.ISPPROF                            
NONVSAM ------- ADCDA.S0W1.SPFLOG1.LIST                            
NONVSAM ------- ADCDB.S0W1.ISPF.ISPPROF                            
...                           
CLUSTER ------- SYS1.VVDS.VC4CFG1                                  
   DATA ------- SYS1.VVDS.VC4CFG1

Which shows there is a data component of the catalog called USERCAT.Z24C.USER, and there is index component called USERCAT.Z24C.USER.CATINDEX.

The catalog has a data component (USERCAT.Z24C.USER) and an index component USERCAT.Z24C.USER.CATINDEX.

Within the catalog are entries for data sets such as ADCDA.S0W1.ISPF.ISPPROF, and system (DFDSS) dataset SYS1.VVDS.VC4CFG1 - which contains information what is on the SMS DASD volume C4CFG1.

One minute networking: TCP buffer sizes

When data flows over a TCPIP connection there are several factors which control the rate at which data can be sent. You can influence some of these factors.

Data is sent as packets typically of size about 1440 bytes – because old hardware could only support this. You could use larger packets, but you may hit a router which chops it into smaller blocks.

The basic TCPIP flow

Consider a Client Server connection. The client application wants to send some data to a server application

  • The client uses send() to put some data into a TCPIP buffer and returns.
  • TCPIP sends some data (a packet) from this buffer, sets a timer and waits.
  • The server receives the data, end sends back an ACK saying so far I have received this many bytes from you.
  • The application on the server does a receive (if there is no data, the application is suspended until data arrives). If there is enough data to satisfy the receive, the application returns, otherwise it is suspended.
  • At the client end, when TCPIP has received the ACK. It no longer needs the data which has just been acknowledged. It can send more data.
  • If no ACK was received and the timer has timed out, TCPIP resend the data.

There are several parts to this:

  • Putting things into the pipe – the send buffer
  • The pipe
  • Getting things from the pipe, the receive buffer

The send buffer

  • TCPIP has a buffer for its use.
  • The application
    • An application does a send() and passes data to TCPIP.
    • If there is space in the TCPIP buffer, the data is moved into the buffer, and the application returns.
    • If there is not enough space for all of the data, enough data is moved to fill the buffer, and the application waits until more space is available in the buffer.
    • When all of the data has been passed to the TCPIP buffer, the application returns, and can do more application work.
  • TCPIP
    • TCPIP takes a chunk of the buffer (a packet) , sends it over the network, and sets a timer.
    • It can then process another chunk of data, and send it over the network, so there are multiple packets in flight.
    • When the far end has passed the data to the application, it sends the ACK back.
    • The local end, when it has received the ACK for a chunk of data, knows the data has been received by TCPIP at the remote end, it no longer needs to keep a copy of the data, and frees up the space on the buffer.

How big a buffer is needed to get good throughput?

The data is held in the TCPIP buffers; waiting to be sent plus the round trip time; from when the data was put into the TCPIP buffer, to getting the ACK back. This could be 10s of milliseconds. Multiple packets can be in-flight (perhaps 10s or 100s) which improves the throughput. So send 10 packets; wait, when the first ACK is received, send another packet etc., so there are always 10 packets in flight.

If the buffer is too small the application has to wait. Increasing the send buffer size will increase throughput up to a point (when the application does not have to wait) after this point making it larger may make no difference.

As more data is in flight, the connection needs a bigger send buffer.

An application can set the send buffer size using the SETSOCKOPT call. If this is not used, then there will be a TCPIP default send buffer size. On z/OS this is the system wide TCPCONFIG TCPSENDBFRSIZE …. parameter.

The default used to default to 16KB, and currently is typically 64KB. There is a TCPIP enhancement which says if the send buffer size is larger than 64KB, then TCPIP can dynamically increase it if it will improve performance. See Outbound Right Sizing(ORS).

Note: If you change the system wide send buffer size (TCPCONFIG TCPSENDBFRSIZE on z/OS), this will affect all applications that do not set the size using SETSOCKOPT. You should test this before putting it into production because it may affect many applications.

The receive buffer

At the receiving end, TCPIP has a buffer. Data from the network is put into this buffer. After the data has been put into the buffer, TCPIP sends back an ACK with three fields saying

  • so far I’ve received this many bytes from you
  • I’ve sent you this many bytes
  • my buffer has space for this many bytes

An application does a receive to get the data, if there is insufficient data to satisfy the receive, the application can wait, or return just the data in the buffers, depending on the options.

If the receive buffer is full, any incoming data will be thrown away. If the application does receive the data, then does lots of processing on the data, followed by receive more data etc, the receive buffer may fill up. Some applications receive the data, give the data to a subtask to process, immediately do another receive, and so try to keep the receive buffer empty.

If the amount of arriving data is larger than the free space in the buffer, TCPIP will return “no space left in the buffer” as part of an ACK. The sender then knows to wait. When the application receives the data, and makes space, “x bytes are available in the buffer” is sent as part of the ACK, and the sender can start sending data again. This “space available” is known as the Window Size, and helps regulate the flow of data.

If you think about this for several minutes, you will realise that there is a time lag between the receive available buffer size going to zero, and the sender receiving the ACK saying no space in receive buffer. Any in-flight packets may get thrown away, or the end application may get all the data from the buffer. The “no space left in receive buffer” tells the sender to stop sending data until there is space in the buffer, and the sender may then reduce the amount of in-flight data.

Having a zero sized window means there is a problem that the application is not getting the data from the buffer fast enough.

How big a receive buffer is needed to get good throughput?

If the buffer is too small the application has to wait, and packets may be thrown away.

An application can set the receive buffer size using the SETSOCKOPT call. If this is not used, then there will be a TCPIP default receive buffer size. On z/OS this is the TCPCONFIG TCPRCVBFRSIZE …. parameter.

The maximum receive buffer size is specified in TCPMAXRCVBUFRSIZE.

If the receive buffer size is greater than 64B, then a performance enhancement called Dynamic Right Sizing(DRS) can come into action which automatically increases the buffer size up to 2MB.

Inside the pipe

I have described the sender side filling the send buffer for the connection, and the application on the receiver side taking data from the connection’s receive buffer. I’ll look at the pipe in between.

Data is send across the network in packets. The packets are usually small – for example 1500 bytes for Ethernet. Some protocols support larger packet sizes. Data send within a z/OS can have 56KB packet sizes. The Maximum Segment Size (mss) is the maximum size of the user data in a packet.

If a packet is too large for a device, it may be cut into smaller chunks and then passed on – or the packet may just be dropped.

The simplest and slowest transmission is send one packet and wait for the ACK, then send another packet.

It is much more efficient to send multiple packets. For example send 10 packets, when the first ACK comes back (saying the first packet has been received), send the next packet and so on, so there are always 10 packets (or less) in the pipe.

The amount of data on the network is limited by the smaller of the send buffer size and the receive window size. This means you need both a big send buffer, and a big receive buffer to get maximum throughput.

The TCP window is the maximum number of bytes that can be sent before the ACK must be received. If the network is unreliable it is better to keep the window small to reduce the amount of data that needs to be resent after a missing ACK.

Where can I get more information?

I wrote a blog post about tuning MQ channels which gives additional information.

How do I display this buffer information?

On z/OS you can use

  • TSO NETSTAT CONFIG command reports the default receive buffer size, the default send buffer size, and the default maximum receive buffer size
  • TSO NETSTAT ALL (IPPORT nnnn where nnnn is the port number.
  • TCPMON on GITHUB to monitor the buffer and window sizes in near real time.

On Linux

You can use the command

  • ss -im -at ‘( dport = :21 )’ which displays information about connections with destination port of 21.
  • ss -im -at ‘( dst = 10.1.1.2 )’ which displays information about connections with destination ip address of 10.1.1.2

Is there more information available about buffers and windows?

There is a lot of information on the web, but it is not usually easy to digest.

I thought this article was clear about the different buffers and windows.

How do I change the buffer sizes?

An application can change them using the SETSOCKOPT call see here options SO_RCVBUF and SO_SNDBUF

With some applications, they have a specific way of setting the buffer sizes

  • MQ for midrange RcvBuffSize etc
  • MQ on z/OS use +cpf RECOVER QMGR(TUNE CHINTCPRBDYNSZ nnnnn)
    +cpf RECOVER QMGR(TUNE CHINTCPSBDYNSZ nnnnn)
  • FTP on Linux -x option

Otherwise the system defaults are used.

Other information provided with display commands

Commands like netstat provide other information

For example

  • round trip time – this is average time in millisecond taken for a packet to be sent over the network, and the ACK is received
  • RoundTripVariance – this gives the spread of the response times. It is the sum of the square of each response time. A measure of the spread of the response times is the standard deviation = sqrt((the variance – average round trip time ** 2) /N) where N is the number (of packets sent). If all the packets have the same round trip time, this will be close to zero.
  • Local 0 window count – the number of times there was 0 space in the receive buffer
  • Remote – window count – the number of times the remote end had 0 space in its receive buffer.

Configuring frr on Linux

frr is a network router for Linux systems.

It works well, and has a lot of good documentation about all of the commands and options, but it does doesn’t have a “getting started” section. It is a bit like getting the wiring diagram for a car, when all you to do is get in and drive the car.

Below are some of the things I stumbled across lessons I learned.

Some later definitions override earlier definitions.

With

router ospf6
  ospf6 router-id 6.6.6.6  
  ospf6 router-id 6.6.6.7

The definition used is 6.6.6.7 because it overrides the earlier 6.6.6.6

interface eno1 
   ipv6 nd prefix 2001:db8:6099::/64
   ipv6 nd prefix 2008::/64

 
interface eno1
   description server2 ospf6
   ipv6 ospf6 instance-id 2

The description is description server2 ospf6 because it was the only one specified.

Both of the nd prefix values are used.

What is used where?

If you want to configure a daemon, you needs to specify parameters in different places.

For example, the ospf6 daemon

router ospf6
  ospf6 router-id 6.6.6.6
...  

interface enp0s31f6
  ipv6 ospf6 area 0.0.0.0

The router ospf6 configuration is for the daemon thread.

The information on the interface…. statement is for each interface. This means all of the configuration information for an interface is under the interface…. section.

To display the ospf6 configuration use

show running-config ospf6

It extracts the ospf6 interesting information from the configuration

Current configuration:
!
frr version 8.1
...
hostname Server
!
debug ospf6 zebra
debug ospf6 interface
!
interface eno1
 description server2 ospzz
 ipv6 ospf6 area 0.0.0.0
 ipv6 ospf6 instance-id 2
 ipv6 ospf6 network point-to-point
exit
!

router ospf6
 ospf6 router-id 6.6.1.1
 redistribute static
 redistribute ripng
exit
!
end

and ignored other information like

debug ospf zebra
debug ospf interface 

interface eno1 
   ipv6 nd prefix 2001:db8:6099::/64
   ipv6 nd prefix 2008::/64

The debug ospf… is ignored because this relates to ospf not to ospf6.

The ipv6 nd is ignored because this is not ospf6 related.

Configuring using vtysh

You can use vtysh to configure your /etc/frr/frr.cntl for example

  • vtysh
  • configure
  • interface vl100
  • ipv6 address 3000::1/64
  • do write
  • quit
  • quite
  • quit

it is a good idea to make a copy of the /etc/frr/frr.conf before you do this.

Show doesn’t always show

You can use the command

show running-config

and that shows you most of what is configured and running.

Note that default values may not be displayed.

When my definitions had 

interface eno1 
   ip ospf hello-interval 11

the show running-configuration gave

interface eno1
 description server ospzz
 ip address 10.1.0.3 peer 10.1.0.2/24
 ip ospf area 0.0.0.0
 ip ospf dead-interval 40
 ip ospf hello-interval 11

When I had ip ospf hello-interval 10 the output did not include ip ospf hello-interval 10 because it was the default value.

You can use sudo vtysh

show running config
write file

to rewrite the /etc/frr/frr.conf control file with the defaults removed, and the frr version line updated.

If you use the command

show ip ospf interface

it gives you the values for each interface such as

Timer intervals configured, Hello 10s, Dead 40s, Wait 40s, Retransmit 5

OSPF defaults

these were in the file lib/libospf.h in the frr source.

 OSPF_MIN_LS_INTERVAL                  5000     /* msec */
 OSPF_MIN_LS_ARRIVAL                   1000     /* in milliseconds */
 OSPF_LSA_INITIAL_AGE                     0      /* useful for debug */
 OSPF_LSA_MAXAGE                       3600
 OSPF_CHECK_AGE                         300
 OSPF_LSA_MAXAGE_DIFF                   900
 OSPF_LS_INFINITY                  0xffffff
 OSPF_DEFAULT_DESTINATION        0x00000000      /* 0.0.0.0 */
 OSPF_INITIAL_SEQUENCE_NUMBER    0x80000001U
 OSPF_MAX_SEQUENCE_NUMBER        0x7fffffffU


/* OSPF interface default values. */
 OSPF_OUTPUT_COST_DEFAULT           10
 OSPF_OUTPUT_COST_INFINITE          UINT16_MAX
 OSPF_ROUTER_DEAD_INTERVAL_DEFAULT  40

 OSPF_ROUTER_DEAD_INTERVAL_MINIMAL   1
 OSPF_HELLO_INTERVAL_DEFAULT        10
 OSPF_ROUTER_PRIORITY_DEFAULT        1
 OSPF_RETRANSMIT_INTERVAL_DEFAULT    5
 OSPF_TRANSMIT_DELAY_DEFAULT         1
 OSPF_DEFAULT_BANDWIDTH           10000  /* Mbps */

 OSPF_DEFAULT_REF_BANDWIDTH      100000  /* Mbps */

 OSPF_POLL_INTERVAL_DEFAULT         60
 OSPF_NEIGHBOR_PRIORITY_DEFAULT      0

 OSPF_MTU_IGNORE_DEFAULT             0
 OSPF_FAST_HELLO_DEFAULT             0

 OSPF_AREA_BACKBONE              0x00000000      /* 0.0.0.0 */
 OSPF_AREA_RANGE_COST_UNSPEC     -1U

 OSPF_AREA_DEFAULT       0
 OSPF_AREA_STUB          1
 OSPF_AREA_NSSA          2
 OSPF_AREA_TYPE_MAX      3

/* SPF Throttling timer values. */
 OSPF_SPF_DELAY_DEFAULT              0
 OSPF_SPF_HOLDTIME_DEFAULT           50
 OSPF_SPF_MAX_HOLDTIME_DEFAULT       5000

 OSPF_LSA_MAXAGE_CHECK_INTERVAL          30
 OSPF_LSA_MAXAGE_REMOVE_DELAY_DEFAULT    60

One minute networks: MAC address

A MAC address is a Media Access Control address. It has two parts, the manufacturer, and the manufacturer’s unique number. For example on my laptop I have an Ethernet socket. I can see from a wireshark trace that a packet is being broadcast with Ethernet address MicroStarInt_e9:31:2a, or 00 d8 61 e9 31 2a in hex. This was created by Micro Start international.

On a different machine the address is LCFCHeFE 36:f4:8a or 8c 16 45 36 f4 8a. This Ethernet adapter has been provided by LCFC Electronics technology, with serial number 36f48a.

Within an Ethernet switch, there are various broadcasts to devices on the switch, such as

ff02::1all nodes
ff02::2all routers
ff02::5all OSPF (Open Shortest Path First) routers

Using wireshark I can see a broadcast with code ff02::2 which is an IPV6 router Solicitation request from 8c:16:45:36:f4:8a. This is basically saying “have any routers been configured on this Ethernet network, if so, please tell me”. I can map the 8c:16:45:36:f4:8a back to the Ethernet adapter LCFCHeFE 36:f4:8a.

Wireshark has logic to map the Ethernet address prefix to the manufacturer, and convert 8c:16:45 to LCFCHeFE.

One minute networks: Switches, routers, hubs and IP addresses

This blog post is similar to my posts under “One Minute MVS” which aim to provide basic knowledge to understand a topic.

I struggled to understand some of the networking concepts. There is a lot of documentation on the internet, but it did not cover the basics.

The concepts below are based on Ethernet and physical connections. Other connection types such as wireless can be used just as well, but I find the Ethernet picture simple to understand.

What is a router?

A router is used

  • to convert from one network protocol to another protocol
  • to connect bits of network together.

Broadband router

I have broadband to my house, it comes from my telecom’s provider.

  • There is a broadband protocol for the connection to the telephone exchange, for example it connects using my house phone number, not IP address.
  • It converts from broadband to wireless and Ethernet protocols for my various devices around the house.
  • I can connect my laptop to the router, and connect to other devices around the house, on a different network.

What is a switch?

Think of a self contained office. An Ethernet switch is a box with physical sockets for plugging Ethernet cables into. Each person’s computer has a unique address (known as a MAC). Each computer is connected by an Ethernet cable to a physical port on the Ethernet switch. If your computer wants to send information to another computer in the office it sends a request to the Ethernet switch, saying send this information to this MAC address. The switch knows which physical port matches the MAC, and sends the data down the cable plugged into the physical port.

With the configuration described so far, a computer cannot get to the outside internet.

What is hub?

A hub is a very dumb switch, it sends the incoming data to all devices, it is not smart enough to work out which devices to send the data to. It is used when there are a small number of connections.

Does each device need a unique IP address?

Within a network or sub network, each device needs a unique IP address. My laptop has IP address 192.168.1.1 within my network. My neighbour’s laptop has the same IP address within her network. They are on totally separate networks and do not interact, and so they can each have the same IP address.

Each device connected to the internet needs a unique IP address, so the back-end systems can send the data to your device.

A router can be clever and make each device attached to the internet look like a unique device

  • A server has a fixed IP and port, so client applications can find it.
  • Each time a client machine starts, it can be given a different IP address, and when it connects to a server it can use a different port.
  • The server usually does not care what IP address and port the client uses.

If the IP the address of my laptop is 192.168.1.1, this is an internal address and cannot be used on the internet. My router has external address 7.7.7.1.

The router can do some clever mapping

  • If I try to connect from my laptop source address 192.168.1.1 port 100 to the outside world, the router can change the source address to 7.7.7.1 port 206, so looking like a port on the router.
  • If I try to connect from my laptop address 192.168.1.1 with a different port, 200, to the outside world, the router can change this address to 7.7.7.1 port 209
  • If I try to connect from my server with a different address 192.168.1.16 port 100 to the outside world, the router can change this address to 7.7.7.1 port 208.

As far as the internet is concerned requests have come from address 7.7.7.1 with three different ports. When the replies come back, the router maps them back to the internal addresses and ports. The ports numbers 206, 209 and 208 could have been any free port on the router. Tomorrow I may get different numbers.

What is a router – routing

In my house the broadband is on a cable. This is plugged into a router. My red Ethernet switch is also plugged into the router, and my blue Ethernet switch is plugged into another physical socket on the router.

When data from the internet arrives, there are routing rules which say

  • If the traffic is destined for the red switch, then send it to the red switch.
  • If the traffic is destined for the blue switch, then send it to the blue switch.
  • If the traffic is destined for any of the following list of addresses, send it on the broadband cable.
  • Otherwise send it on the broadband cable.

At the far end of the broadband cable is a telephone exchange. This is different sort of router which says if the traffic is for the phone number 01856…. then send to to my house.

The next level of detail

Each computer in the switch is given an IP address, such as 192.168.22.5, another might be 192.168.22.6, where the last number changes with the different computers.

The router has configuration information saying data for 192.168.22.* send it to the red switch.
The blue Ethernet switch has addresses 10.1.1.*

My router has 3 connections, one for broadband, one for the red switch, and one for the blue switch.

If you physically pick up my switch. All of the Ethernet cables coming out of it are part of a subnet. They all have a similar IP address (192.168.1.*), they are in the same subnet.

My router has the following definitions

  • The physical port to the router, has address 192.168.22.25
  • The physical port to the blue router has address 10.1.1.6
  • The physical port to my broadband router is address 192.168.1.222

The top part of these addresses are all different. They are different subnets.

Router routing

If we have a configuration like

Where internet traffic comes into A for the laptop

For sending data to the laptop with IP address 1.1.1.1, you can configure the network

  • On router A. Send traffic for 1.1.1.* to router B. If B is not available send traffic for 1.1.1.* to router C. This provides dual path, or a backup route.
  • On router B. Send traffic for 1.1.1.* to router D.
  • On router C. Send traffic for 1.1.1.* to router D.

Similarly you can configure router D to say to get to the internet you can go via B or C.

Addresses

You could have a configuration like

Where …

  • the red circle has a laptop connected directly to the router. All of the addresses begin with B. The router end of the connection has an address B.2, where B could be 10.1.1, or 192.168.1 etc
  • the blue circle has an Ethernet switch (SW1) attached to the router. All of the elements have an address A…. where A is different to B. The numbers after A are all different; a laptop with address A.3, a laptop with address A.6, the connection to the router has address A.2, and the router end of the connection has address A.8
  • the green circle is is similar to the blue circle, it uses switch SW2. The value of C is different to A and to B.
  • the yellow circle has the connection to the internet. I is the external address of the router and may be something like 9.8.7.23

Let A be 10.1.1 B be 10.2.2 and C be 10.3.3. I could pick any values as long as A, B and C are different, and different to any addresses on the internet.

Within the routing tables in the router I could have

  • All traffic for the address 10.2.2.9 (B.9), send down 10.2.2.2 (B.2). I could also say any traffic for address starting 10.2.2.* send down 10.2.2.2 (B2).
  • All traffic for the address 10.1.1.* , send down 10.1.1.2 (A.2). This is a range of addresses.
  • All traffic for the address 10.3.3.* , send down 10.3.3.8 (C.2). This is a range of addresses.

If I decide to change 10.2.2.* to 11.2.2.* I have to change all of the laptops and the switch within the blue subnet, and the router’s routing tables to reflect the change.

Technological advances

It used to be that a router and switch were hardware devices. These days many routers are just computers running Linux with lots of Ethernet ports.

One minute MVS: Networking subnets.

I’ve understood and used subnets, (in a hand waving way), but found it hard to write down what they are good for, and why we have them. There are many explanations on the web but they all seemed to describe how to use subnets, and not why we need them. Some of what I say below, may be strictly not true, but I hope it gives the right concepts.

  • You can use an Ethernet cable to join two machines. This is not very interesting.
  • You can have an Ethernet router. You plug the Ethernet cable from your machine to one of the ports on the Ethernet router.
  • The Ethernet router has devices attached to it with addresses such as 192.168.1.160, 192.168.1.24, 192.168.1.74. The router handles traffic for 192.168.1.* The IP address is 32 bits long, and the router is configured so that if the top 24 bits of an address are 192.168.1, then pass the traffic to the router. This is written as 192.168.1.0/24. The remaining 8 bits can be used for devices attached to the router, so almost 256 devices. (192.168.1.0 and 192.168.1.255 are reserved).
  • If you had a large building you could configure a router with address 192.169/16 and have 65,000+ devices attached to it. This may not be a good idea.
    • The router sends out management packets to all devices in the subnet saying, for example “does anyone have this IP address”. With many devices the router could spend all its time processing these management packets, and not handling user data
    • You may want to segregate different areas, so addresses 192.168.1.* is for the first floor, and 192.168.2.* is for the second floor. If you want to have a firewall for the first floor it is much easier configuring all traffic going to 192.168.1.* rather than for some machines within 192.168.* and so all users are using the firewall – which may not be what you want.
    • Each floor has a confidential printer. It is easier to configure the printer so that only machines with the same subnet address, IP address 192.168.1.* can send print files to the printer on 192.168.1.22, rather than filter out users on the second floor.
  • With IP V6 there are 128 bits available for subnetting. Mostly a subnet of /64 is used. I have an address 2a00:9999:8888:7777:a0cd:ec92:bceb:91ab/64 so 2a00:9999:8888:7777 is the address of my router (64 bits), and the device on the router is currently a0cd:ec92:bceb:91ab (64 bits).

Basic connectivity

Single point to point cable

My laptop is connected to my server by an Ethernet cable.

I’ve defined the address at each end 10.1.0.2/24 at the laptop and 10.1.0.3/24 at the server. I can ping between the two machines. When I changed the server to have 12.1.0.3/24 there was no connectivity – because they were in different subnets.

Wireless connection – IPV4

My system was configured automatically to have the laptop 192.168.1.222/24 and the server 192.168.1.222/24. These are the same subnet, so traffic goes from my laptop up the wireless connection to the wireless router, and to the server over the wireless connection.

Wireless connection – IPV6

My system was configured automatically to have the laptop a prefix (subnet) of fe80 and specific address c82d:b94c:21fa:3d1c with this this subnet. The server had prefix (subnet) fe80 and specific address c82d:b94c:21fa:3d1c.

The default routing is via device (the wireless router) with prefix (subnet) fe80 and address c82d:b94c:21fa:3d1. These are both “internal to the router” addresses.

Today my laptop also has IP address 2a00:9999:8888:7777:a0cd:ec92:bceb:91ab/64 and my server has address2a00:9999:8888:7777:605a:2d22:5daf:53d7/64. These can be used to contact sites on the internet, because they are external addresses.

Getting out of the subnet.

My server has a connection over virtual Ethernet to z/OS. The server end of this link has address 10.1.3.1/24. If I use wireless connection from my laptop to the server, I cannot easily access this link, because the wireless router does not know about 10.1.3.1 – and I have no way of configuring it.

On Linux I can configure the server to be a software router (radvd), and have a physical Ethernet cable to the it from my laptop. This way I can control the IP routing to and from the server.

You can also use a bridge … but that is an advanced topic.