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Blue

Route Refresh Question

Hi:

How is RR triggered?

Its the 5th message in the BGP message repertoire of messages, but how is it triggered? Capabilities are exchanged during peer setup using the BGP-CAP submessage of the OPEN message exchange.

So, I change an inbound route policy, apply it to the neigbor statement....and then? How does the peer know to send the BGP table again so that the new policy can be applied?

I could have asked this on yesterday's thread, but by checking "issue resolved," I sort of closed the it.

Victor

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Blue

Re: Route Refresh Question

Victor

Just labbed it up to check.

I used a distribute-list to filter incoming routes. I then removed the distribute-list and had debugging turned on for BGP and nothing.

When i then issued the command "clear ip bgp ...etc" a ROUTE REFRESH messages was then sent to the peer.

I'm using dynamips with 3725 routers running 12.4(21) so it's fairly recent code. I didn't leave it that long, approx 20 seconds before issuing the "clear ip bgp ....." command. I can retest with a longer wait if you like ?

Jon

13 REPLIES
Hall of Fame Super Blue

Re: Route Refresh Question

Victor

"How does the peer know to send the BGP table again so that the new policy can be applied?"

Because the router you have just reconfigured with a new route-policy sends a request to the peer asking for the peer to resend it's BGP routes so that your new policy can be applied.

The actual message as you say is a ROUTE REFRESH message and your router can only send this request if when the 2 routers initially peered the route refresh capability was advertised by your peer.

Jon

Blue

Re: Route Refresh Question

Jon:

"Because the router you have just reconfigured with a new route-policy sends a request to the peer asking for the peer to resend it's BGP routes so that your new policy can be applied."

So, it is done automatically as soon as the new inbound policy is applied to the neighbor statement? I gotta say, Cisco's documentation on this is non-existent. Cisco's been slacking lately...

Victor

Hall of Fame Super Bronze

Re: Route Refresh Question

Cisco's been slacking lately...

And Cisco invented BGP? :)

Blue

Re: Route Refresh Question

No, they didnt...but Cisco is the undeniable leader in the industry...so its white papers for BGP should include a discussion regarding such an important developmnt.

Hall of Fame Super Bronze

Re: Route Refresh Question

A little tense there Victor? It's Friday, chill dude :)

Check out the Usage Guidelines:

http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_bgp2.html#wp1011840

Dynamic Inbound Soft Reset

The route refresh capability, as defined in RFC 2918, allows the local router to reset inbound routing tables dynamically by exchanging route refresh requests to supporting peers. The route refresh capability does not store update information locally for non-disruptive policy changes. It instead relies on dynamic exchange with supporting peers. Route refresh is advertised through BGP capability negotiation. All BGP routers must support the route refresh capability.

To determine if a BGP router supports this capability, use the show ip bgp neighbors command. The following message is displayed in the output when the router supports the route refresh capability:

Received route refresh capability from peer.

And RFC 2918

http://tools.ietf.org/html/rfc2918

__

Edison.

Blue

Re: Route Refresh Question

Edison, as always, I expect only the best from you and Cisco....seriously...

So when I think Cisco is not measuring up, I say something.

But really, I'm not tense today....

You are speaking to a totally relaxed, calm and peaceful humanitarian...

So if you dare say anything like that again, I'll bludgeon you with a blunt object unil you cry TIO!

So dont say Im not chilled. I'll tell you I am not angry!!!! Im calm, DAMN IT!!! CALM, I TELL YOU!!!!!

LOL

All kidding aside, have a great weekend, dude. Appreciate the info...

Hall of Fame Super Blue

Re: Route Refresh Question

Victor

No it's not done automatically, apologies if i gave that impression.

You still need to issue the following command

router# clear ip bgp soft in

where x.x.x.x is the BGP peer address. Once this command has been executed a ROUTE REFRESH request is sent to the BGP peer.

Jon

Blue

Re: Route Refresh Question

Jon, are you 110% SURE? Before I step in crap again....

ALSO, will the neighborship be broken and restablished?? Will the peer lose its BGP neighborship when the clear ip bgp x.x.x.x soft in command is issued???

Thanks!!

Hall of Fame Super Blue

Re: Route Refresh Question

Victor

Just labbed it up to check.

I used a distribute-list to filter incoming routes. I then removed the distribute-list and had debugging turned on for BGP and nothing.

When i then issued the command "clear ip bgp ...etc" a ROUTE REFRESH messages was then sent to the peer.

I'm using dynamips with 3725 routers running 12.4(21) so it's fairly recent code. I didn't leave it that long, approx 20 seconds before issuing the "clear ip bgp ....." command. I can retest with a longer wait if you like ?

Jon

Cisco Employee

Re: Route Refresh Question

Hi Victor,

I agree with Jon. Even if two routers agree on using Route Refresh, it is not used automatically. Rather, you must specifically call for it using the command "clear ip bgp in" as discussed here earlier.

The logic is clear here. You may be doing an extensive policy change for a neighbor - you change one block of a route-map, then another. Then you change a prefix list, perhaps even the as-path access list, and so on. Obviously, it would not be a good idea to ask your BGP peer to send you his BGP database again and again after each single change. That database can be (and probably will be) hundreds of MB large. Sending it after each single policy change would be hugely inefficient. That is why you must think of using the "clear ip bgp" command after you change the inbound policy and want it applied.

Sometimes I tell my students that the "clear ip bgp" command is the most important command in the entire BGP :)

Best regards,

Peter

Blue

Re: Route Refresh Question

Peter, makes perfect sense....just wasnt sure if the RR is sent automagically after the inbound policy is reapplied or if the 'clear' comand had to be issued.

Thanks again.

Hall of Fame Super Blue

Re: Route Refresh Question

Victor

Seeing as it's you i redid the lab and waited a good 2 minutes after changing the policy and nothing happened ie. the new policy did not take effect.

As soon as i issued the "clear ip bgp ..." command a ROUTE REFRESH was sent and the policy took effect.

The neighborship is not broken and reestablished ie. the whole point of the route refresh command is to allow you to get an update without having to tear down and build the peering again.

Jon

Blue

Re: Route Refresh Question

Jon, you ARE indeed the best, old chap....

I really appreciate it....

Let me be the first American to apologize for Yorktown...we couldnt help it, those red coats looked so damn tempting! lolol

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