Routing Bit Set on LSA for NX-OS

Plinio Brandao · ‎07-01-2015

Hi everybody,

I was doing some configurations using Nexus 7k with OSPF and I saw a point that I wasn't able to find a document with an answer for this.

I know that OSPF in NX-OS has its peculiarities, but I trying to figure out the lack of the Routing Bit Set information on the LSA output command.

Below, we can see the outputs:

N7K-01# sh ip route 10.0.11.0
IP Route Table for VRF "default"
'*' denotes best ucast next-hop
'**' denotes best mcast next-hop
'[x/y]' denotes [preference/metric]
'%<string>' in via output denotes VRF <string>

10.0.11.0/24, ubest/mbest: 1/0
    *via 10.19.0.1, Po21, [110/20], 1w0d, ospf-10, type-2
--------------
N7K-01# sh ip ospf database external 10.0.11.0 
        OSPF Router with ID (10.19.0.2) (Process ID 10 VRF default)

                Type-5 AS External Link States 

Link ID         ADV Router      Age        Seq#       Checksum Tag
10.0.11.0       10.19.0.1      852        0x8000048f 0xcd67    0
--------------
N7K-01# sh ip ospf database external 10.0.11.0 detail 
        OSPF Router with ID (10.19.0.2) (Process ID 10 VRF default)

                Type-5 AS External Link States 

   LS age: 855
   Options: 0x2 (No TOS-capability, No DC)
   LS Type: Type-5 AS-External
   Link State ID: 10.0.11.0 (Network address)
   Advertising Router: 10.19.0.1
   LS Seq Number: 0x8000048f
   Checksum: 0xcd67
   Length: 36
   Network Mask: /24
         Metric Type: 2 (Larger than any link state path)
         TOS: 0
         Metric: 20
         Forward Address: 10.7.19.6
         External Route Tag: 0

This is a normal behaviour from NX-OS? We should expect this?

If we compare with IOS, we can see something like that:

R1#sh ip ospf data ex 10.10.4.0

            OSPF Router with ID (10.10.12.1) (Process ID 1)

                Type-5 AS External Link States

  Routing Bit Set on this LSA
  LS age: 243
  Options: (No TOS-capability, DC)
  LS Type: AS External Link
  Link State ID: 10.10.4.0 (External Network Number )
  Advertising Router: 10.10.23.3
  LS Seq Number: 80000002
  Checksum: 0xF66E
  Length: 36
  Network Mask: /24
        Metric Type: 2 (Larger than any link state path)
        TOS: 0 
        Metric: 1 
        Forward Address: 10.10.234.4
        External Route Tag: 0

Thank you very much in advance.

Regards,

Plínio

Plinio Brandao · ‎07-06-2015

Hi,

Just a feedback: I received this answer from another topic:

From the book “Routing TCP/IP Volume 1”, 2^nd Edition:

The routing bit is not a part of the LSA itself; it is an internal maintenance bit used by IOS indicating that the route to the destination advertised by this LSA is valid. So when you see "Routing Bit Set on this LSA", it means that the route to this destination is in the routing table.

So I would say it is something specific to IOS and not implemented in NX-OS.