BGP attributes through IGP
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.
On (2014-03-06 10:37 -0500), Bryan Ashley wrote:
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.
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. -- ++ytti
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. On Thu, Mar 6, 2014 at 4:09 PM, Saku Ytti <saku@ytti.fi> wrote:
On (2014-03-06 10:37 -0500), Bryan Ashley wrote:
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.
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.
-- ++ytti
iBGP over GRE? On Thu, Mar 6, 2014 at 2:58 PM, Bryan Ashley <bja8180@gmail.com> wrote:
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.
On Thu, Mar 6, 2014 at 4:09 PM, Saku Ytti <saku@ytti.fi> wrote:
On (2014-03-06 10:37 -0500), Bryan Ashley wrote:
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.
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.
-- ++ytti
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 On Thu, Mar 6, 2014 at 6:19 PM, Glen Turner <gdt@gdt.id.au> wrote:
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
On (2014-03-07 10:49 +1030), Glen Turner wrote:
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. -- ++ytti
participants (5)
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Blake Dunlap -
Bryan Ashley -
Elliot Finley -
Glen Turner -
Saku Ytti