[j-nsp] Error BGP RECV Notification code 2 (Open Message Error) subcode 7 (unsupported capability)

[sthaug at nethelp.no]

>  M10i already has many peers that support *2 byte asn only* and is running
> without any issues, but *why it is not able to negotiate with Maipu to make
> the peer up without disabling the 4byte asn capability*.
> 
> ASFAIK, 4 byte ASN or AS4_PATH is an optional transitive attribute unlike
> AS_PATH mandatory attribute. My asmuntion is BGP new_speaker may send
> AS4_PATH to its neighbor an OPEN message with capability check, if fail it
> should have to use AS_PATH or 2 byte to negotiate to its OLD-BGP speakers
> and  make the peer up.
> 
> *The question is why JunOs failed with Maipu ?

No, the correct question is, why did Maipu fail? 

JunOS announces 4 byte ASN capability in all reasonably new versions.
Some peers cannot handle this, Maipu seems to be among them.

We have had to disable the 4 byte ASN capability announcement towards
a few customers having BGP speaking firewalls and similar stuff.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no