BGP UPDATE message 23 bytes

[leoalb]

When a node starts sends to its neighbors a BGP update with Unfeasible Routes Length = 0 and the value of Total Path Attribute Length = 0. (and another one with the prefixes that it knows)
I'm using the BGP ASN config for Routing in Large-Scale Data Centers (https://www.rfc-editor.org/rfc/rfc7938.html).
What is this behavior due to? implementation or BGP behavior?
Thanks!

[donaldsharp]

can you give a bit more specific information about what is going on? Configuration and some examples? I am not sure what you are asking or seeing.

[leoalb]

sure!

• Topology:
  R21(ASN1) R22(ASN1)
  | X |
  R11(ASN2) R12(ASN3)
  | |
  200.0.0.0/24 200.0.1.0/24

• BGP config
  R11
  ...
  router bgp 64512
  timers bgp 3 9
  bgp router-id 192.168.0.1
  no bgp ebgp-requires-policy
  bgp bestpath as-path multipath-relax
  bgp bestpath compare-routerid

neighbor TOR peer-group
neighbor TOR remote-as external
neighbor TOR advertisement-interval 0
neighbor TOR timers connect 5
neighbor eth0 interface peer-group TOR
neighbor eth1 interface peer-group TOR

address-family ipv4 unicast
neighbor TOR activate
network 200.0.0.0/24
maximum-paths 64
exit-address-family

• Question: is it normal that when R11 shows up it sends a BGP Update empty, i.e., a BPG message with a total length of 23bytes (without Withdrawn Routes or Paths)? (And after that the Update with the expected 200.0.0.0/24 announce)

[ton31337]

Can you send us pcap?

[leoalb]

R11_eth0.pcap.zip

Here is the capture for the link R11<--->R21