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.

Understanding IP V6 NETSTAT ROUTE on z/OS information

I struggled with the output of the TSO NETSTAT ROUTE command.

Below is an example from my system. The IBM documentation is here

IPv6 Destinations 
DestIP:   Default 
  Gw:     2001:db8:1::3 
  Intf:   IFPORTCP6         Refcnt:  0000000000 
  Flgs:   UGS               MTU:     1492 
DestIP:   ::1/128 
  Gw:     :: 
  Intf:   LOOPBACK6         Refcnt:  0000000000 
  Flgs:   UH                MTU:     65535 
DestIP:   2001:db8::/64 
  Gw:     :: 
  Intf:   IFPORTCP6         Refcnt:  0000000000 
  Flgs:   US                MTU:     5000 
DestIP:   2001:db8:1::/64 
  Gw:     :: 
  Intf:   IFPORTCP6         Refcnt:  0000000000 
  Flgs:   UD                MTU:     9000 
DestIP:   2001:db8:1::3/128 
  Gw:     :: 
  Intf:   IFPORTCP6         Refcnt:  0000000000 
  Flgs:   UHS               MTU:     5000 

DestIP: Default this is statically set up with default6

Gw: 2001:db8:1::3 This is (one of) the IP address at the remote end of the connection.

Intf: IFPORTCP6 The z/OS interface name is IFPORTCP6

The flags are

U – The route is up.

G – The route uses a gateway.

H – The route is to a host rather than to a network.

S – The route is a static route not replaceable by a routing daemon or router advertisements (IPv6).

D – The route was created dynamically by ICMP processing or router advertisements (IPv6) (possibly OMPROUTE).

DestIP: 2001:db8::/64 This is for IP addresses 2001:0DB8:0000:0000:something there are 64 bits in the significant part of the address. This applies to 2001:0DB8:0:0:0:0:0:99 and 2001:0DB8:0:0:FFFF:0:0:99 for example

DestIP: 2001:db8:1::3/128 This says all 128 bits are significant in the address. This is the 2001:db8:0:0:0:0:0:3 and no other address.

RefCnt Reference count – the current number of active users for the route. See below.

Where does an entry come from?

  • An entry can be statically configured between BEGINRoutes… ENDoutes.
  • An entry can be dynamically configured from an adjacent system. For example
    • a prefix entry when using radvd – this defines IP address ranges into or through the z/OS host
    • a route entry when using radvd, this defines IP address ranges going off the host, to the other end of the connection.
  • An entry be generated dynamically from OSPF and RIP. On z/OS these are usually configured with the OMPROUTE address space. See below.

A statically defined entry has an S in the Flgs

A dynamic entry has a D in the Flgs -sometimes – see below.

Why does Gw: sometimes have a value?

Gw: has a value when

  • it was specified in the static definitions
  • the DestIP entry was created dynamically, for example as a route …{} statement in radvd. This is an output entry, so the Gw: is part of the definition.

Note: a radvd prefix… {} entry is inbound, so the gateway is irrelevant.

I see this as it is only relevant for connections out of z/OS. When traffic comes into the host, you do not care which gateway it came from.

What does refcnt mean for a DestIP?

The documentation it says “Reference count (RefCnt): The current number of active users for the route.”

When I pinged z/OS ten times from 2001:db8::7, the RefCnt for DestIP: 2001:db8::/80 increased by 10.

When I pinged z/OS ten times from another address, the RefCnt values were unchanged.

Issuing a traceroute to the system did not increment any values.

I could find no active connections to this interface, so all in all this field is bit of a mystery.

The Linux documentation says The reference count (i.e. attached processes via this socket), so the z/OS meaning may be a partial historical count of usage rather than the number of active users.

What is the default value?

This was a surprise. I had defined a static route using default6, and this was in the netstat route display output.

When I used

tso netstat route radv

to display the routes added via Router Advertisement it gave me a list including a Default.

IPv6 Destinations 
DestIP:   Default 
  Gw:     fe80::dce0:8fff:fe42:127f 
  Intf:   IFPORTCP6         MTU:  0 
DestIP:   2001:db8::/80 
  Gw:     fe80::dce0:8fff:fe42:127f 
  Intf:   IFPORTCP6         MTU:  0 
DestIP:   2001:db8:0:0:1::/80 
  Gw:     :: 
  Intf:   IFPORTCP6         MTU:  0 
DestIP:   2001:db9::/32 
  Gw:     fe80::dce0:8fff:fe42:127f 
  Intf:   IFPORTCP6         MTU:  0 
DestIP:   2002:db8::/64 
  Gw:     fe80::dce0:8fff:fe42:127f 
  Intf:   IFPORTCP6         MTU:  0 

If the Router Advertisment data has AdvDefaultLifetime > 0 for the interface then a “Default” is generated, else no default is generated.

The wireshark trace has

Internet Control Message Protocol v6
    Type: Router Advertisement (134)
    ...
    Cur hop limit: 64
    Flags: 0xc0, Managed address configuration, ...
    Router lifetime (s): 0 

The MTU value is what was passed in via the RA data. Change this value in the radvd configuration, and the z/OS value changes.

When I removed my statically defined default6, this default became active with

DestIP:   Default 
  Gw:     fe80::dce0:8fff:fe42:127f 
  Intf:   IFPORTCP6         Refcnt:  0000000000 
  Flgs:   UGD               MTU:     9000 

Note: It seems you can have only one active Default, even with IPCONIG6 MULIPATH option. I do not know which default becomes active if you have more than one dynamically defined

The detail option

If you use TSO NETSTAT ROUTE DETAIL you get additional information.

Metric: 00000001 
MVS Specific Configured Parameters: 
  MaxReTransmitTime:  120.000   MinReTransmitTime: 0.500 
  RoundTripGain:      0.125     VarianceGain:      0.250 
  VarianceMultiplier: 2.000     DelayAcks:         Yes d

These numbers look like defaults, and I got them even when not traffic had flowed over the connection.

OMPROUTE

OMPROUTE can

  • Provides some “dynamic” information about default IP6 routes
  • It listens to messages from other routers, and can update the routing tables

Sometimes

Without OMPROUTE, routes that were dynamically created, for example using radvd on Linx, which broadcast z/OS address ranges to z/OS, and advertised “come to me for these address ranges”.

These could be seen as Dynamic, for example the D in UD below.

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

If you start OMPROUTE, the “Dynamic address” now come out as “C”

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