Greetings all - first time caller long time listener.
I came across a scenario the other day which got my wheels turning a bit
and wanted to reach out and see how others are handling this besides what I
would think to be the obvious.
Scenario: R1->R2->R3->R4
R1->R2 eBGP
R2->R3 OSPF
R3->R4 eBGP
Essentially what I want to do is be able to carry BGP attributes through
OSPF so that remote end sees the full AS-PATH, ORIGIN, etc. The easy
answer here is iBGP across OSPF however the wrinkle is this can't be done.
Its a long story and one in which we are currently fighting however
suffice it to say for the moment this option is out.
My searches have come up a little short however I found a couple references
to using automatic-tag and as-path tag to carry this through. I cant seem
to find any Junos reference information on this so wanted to reach out to
the ether and see if others have faced this situation before or have any
other recommendations on solutions.
Responses on or off list is much appreciated.
I don't think JunOS supports this.
It's bit of hack at any rate. It's not transporting AS_PATH, it's transporting
single 16b ASN.
It's essentially abusing (some what well-defined and interoperable abuse) 32b
tag field for this purpose.
Maybe you could try to do some of this manually, set some tags, which trigger
'set then origin x', as-path-expand/prepend might be more challenging.
Recommendation for solution might be easier with rationale why you need to
transport origin+aspath over IGP.
so this scenario was a much more scaled down version of the actual
topology. Basically I have a "gap" of routers that I don't manage or have
access to in between mine running eBGP. We are collecting some metrics and
doing monitoring on the AS-PATH of the routes received, among other
attributes, for both ends so losing some of this information is a problem.
Again, I know the right answer here is to run iBGP across the IGP and I am
fighting that fight but it got me looking for alternative solutions and
figured I would see if anyone else ever had to come up with a creative
solution before.
Saku Ytti wrote:
It's essentially abusing (some what well-defined and interoperable abuse) 32b
tag field for this purpose.
That's pretty much what the OSPF tag and the BGP's synchronisation with OSPF were originally intended for.
However it's pretty much a design misfeature and you'd be happier with iBGP over a tunnel
-glen
Mpls, GRE, line gun...
At some point, you want to stop beginning technical designs with "Doctor!
Doctor! It hurts when I do this. What can I do?"
The answer doesn't generally change, no matter how many times it's asked.
-Blake
That's pretty much what the OSPF tag and the BGP's synchronisation with OSPF were originally intended for.
1403 (1364) is historic and never referenced by OSPF standard. Original
intention for external tag is unspecified information carried between AS
borders.
However it's pretty much a design misfeature and you'd be happier with iBGP over a tunnel
Agreed. If this is common requirement, nothing stopping figuring out new
LSA/LSP to properly carry BGP information. Of course won't be solution for
near-term, unless OP controls the edge and uses open source implementation, in
which case he might send this information in opaque LSA.