From: ccie2be (ccie2be@nyc.rr.com)
Date: Fri May 27 2005 - 12:52:32 GMT-3
Mark,
To be precise, add another router to AS 3, call it R4.
Create a ebgp peering between R1 and R3 and an ebgp peering between R2 and
R4 and, of course, an ibgp peering between R1 and R2.
Now, both R1 and R2 should have 2 bgp paths to routes learned from AS 3: 1
path via the ibgp peer and another path via directly connected ebgp peer.
Now, configure either R1 or R2, your choice, to load balance on a per packet
basis to routes learned from AS 3.
Also, consider both R3 and R4 backbone routers to which you don't have
access so all config's are done on either R1 or R2 or some combo.
Tim
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Mark
Lasarko
Sent: Friday, May 27, 2005 11:32 AM
To: 'GroupStudy'
Subject: Re: BGP Load-balancing paths
I don't have the Vol2 WB, but this sounds interesting.
(AS12) R1 - - - -
| \
| |
| R3 (AS3)
| |
| /
(AS12) R2 - - - -
R1 & R2 have an iBGP peering established (AS12)
Both are also peered to R3 via eBGP (AS3)
Is this the topology?
If so, the goal is to load-balance (or share?) between the eBGP and iBGP
connections?
Perhaps R3 offers some routes and we see both paths not only in the BGP
table,
but also the routing table...
And the catch is you can't route-map your way out of this :)
Let me know if I'm following you guys - I'd like to lab this up!
Cheers,
~M
>>> "Sean C" <Upp_and_Upp@hotmail.com> 05/27/05 10:50 AM >>>
Hi Tim,
I agree, if the Brian's have it in one of their labs, there's got to be a
solution. I'll never forget at one of my lab attempts at RTP - during lunch
the proctor mocked us by saying, to effect - 'Why you guys all nervous? All
the answers are in front of you - all the commands are in the router! It's
not like we're making commands up. And we even gave you the CD'. So,
you're right, there has to be a solution.
I assume you are attempting tasks 5.36-5.38. I haven't attempted that lab
yet. Quickly reviewing it, I was going to suggest some type of route-map
till I read the last task to not use any type of dynamic routing mechanism.
Then I was thinking the new feature for eBGP and iBGP load-balancing:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122
t
/122t4/fteibmpl.htm#wp1027129
Until I read that it's only for MPLS networks-VPNs.
So, I don't know what to suggest off the top of my head. And I can hear
that proctor mocking me right now!
Sean
----- Original Message -----
From: "ccie2be" <ccie2be@nyc.rr.com>
To: "'Sean C'" <Upp_and_Upp@hotmail.com>; "'GroupStudy'"
<ccielab@groupstudy.com>
Sent: Friday, May 27, 2005 10:08 AM
Subject: RE: BGP Load-balancing betw ibgp and ebgp paths
> Thanks, Sean.
>
> My mistake re: AD. You're right, ibgp AD = 200
>
> And, I agree with you that even if the AD of both the ibgp and ebgp
> learned
> route are the same, one route will still be an ebgp route and the other
> route will still be an ibgp route.
>
> And, as a result, BGP will always choose the ebgp route for entry into the
> route table.
>
> The way I understand the BGP decision process, BGP uses this process to
> determine which routes get "promoted" into the route table.
>
> If either the maximum-paths or the maximum-paths ibgp command is
> configured,
> then multiple routes can be "promoted" into the route table.
>
> So, although using the backdoor command is an intriguing idea, I don't
> think
> this will result in load balancing between the i and e bgp learned routes
> because even if they both have the same AD, BGP will always promote an e
> bgp
> path over an i bgp path - at least, that's what I think.
>
> But, on the other hand, I also believe there must be a way to achieve this
> since this problem comes from an IE lab (Vol 2, Lab 6 for those of you who
> have this workbook.) and I don't think the Brian's would have us a do a
> task
> that's impossible to do.
>
> So, the mystery continues.
>
> Thanks, Tim
>
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Sean
> C
> Sent: Friday, May 27, 2005 9:48 AM
> To: GroupStudy
> Subject: Re: BGP Load-balancing betw ibgp and ebgp paths
>
> Hey Tim,
>
> Hold on a moment -
> iBGP AD is 200
> eBGP AD is 20.
> external EIGRP AD is 170 (perhaps that is what you're thinking of).
>
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094195
> .shtml#topic2
>
> Using the BGP network backdoor command will change the AD of the eBGP
> route
> to an AD of 200 - so the eBGP prefix AD will be equal to the AD of an iBGP
> prefix. But please understand, the backdoor command wasn't created to
> equal
>
> the route selection of an eBGP and a iBGP route. Like you wrote, all
> things
>
> being equal, the router will still take choose the eBGP route over the
> iBGP
> route - even if at an AD of 200. The backdoor command was created so the
> router will now select an IGP route (not necessarily an iBGP route) over
> an
> eBGP prefix with the default AD of 20.
>
http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123cgcr/iprr
> p_r/ip2_n1g.htm#wp1041089
>
> HTH,
> Sean
> ----- Original Message -----
> From: "ccie2be" <ccie2be@nyc.rr.com>
> To: "'CCIE6296'" <ccie6296@aces-star.com>; "'Group Study'"
> <ccielab@groupstudy.com>
> Sent: Friday, May 27, 2005 8:54 AM
> Subject: RE: BGP Load-balancing betw ibgp and ebgp paths
>
>
>> Hi,
>>
>> Thanks for that idea. It's a very interesting idea but I'm not sure this
>> will work. Do you know for sure? Have you tested this? At the moment,
>> I
>> can't test this.
>>
>> Here's my thinking:
>>
>> A bgp router knows through it's configuration which peers are ibgp or
>> ebgp.
>> Because it knows that, I suspect it uses that knowledge to decide what AD
>> to
>> assign to routes it learns from its peers. And, if it learns a route
>> from
>> an ibgp peer, it assigns it an AD of 170. But, if it learns a route from
>> an
>> ebgp peer, it assigns it an AD of 20.
>>
>> So, I can't imagine that manually changing the AD of ibgp learned routes
>> will enable load balancing between ibgp and ebgp routes but I do like
>> your
>> idea. And, maybe for some reason I can't think of it would work.
>>
>> Thanks, Tim
>>
>> -----Original Message-----
>> From: CCIE6296 [mailto:ccie6296@aces-star.com]
>> Sent: Friday, May 27, 2005 8:11 AM
>> To: 'ccie2be'; 'Group Study'
>> Subject: RE: BGP Load-balancing betw ibgp and ebgp paths
>>
>> Hi Tim,
>>
>> Use the backdoor command so that the AD for the route learn is same for
>> both
>> iBGP and eBGP.
>>
>> Cheers!
>> csyeo
>>
>>
>> CS Yeo
>> CCIE6296, CISSP, PMP, MCSE
>> http://www.aces-star.com
>> Your Asia rack rental source.
>> Ace the CCIE lab
>>
>> -----Original Message-----
>> From: ccie2be [mailto:ccie2be@nyc.rr.com]
>> Sent: Friday, May 27, 2005 4:58 AM
>> To: Group Study
>> Subject: BGP Load-balancing betw ibgp and ebgp paths
>>
>> Hi guys,
>>
>> I now know how to configure BGP to load-balance between paths learned
>> from
>> either multiple ebgp peers or from multiple ibgp peers.
>>
>> maximum-paths # --- for ebgp peers
>>
>> maximum-paths ibgp # -- for ibgp peers
>>
>>
>> But, how is load balancing configured when the same route is learned from
>> both an ibgp and an ebgp peer?
>>
>> I looked at all the bgp commands available under the bgp process but none
>> appear to do the trick.
>>
>> Any ideas?
>>
>> TIA, Tim
>>
>> R6(config-router)#bgp ?
>> always-compare-med Allow comparing MED from different neighbors
>> bestpath Change the default bestpath selection
>> client-to-client Configure client to client route reflection
>> cluster-id Configure Route-Reflector Cluster-id
>> confederation AS confederation parameters
>> dampening Enable route-flap dampening
>> default Configure BGP defaults
>> deterministic-med Pick the best-MED path among paths advertised
>> from
>> the neighboring AS
>> dmzlink-bw Use DMZ Link Bandwidth as weight for BGP
>> multipaths
>> fast-external-fallover Immediately reset session if a link to a
>> directly
>> connected external peer goes down
>> inject-map Routemap which specifies prefixes to inject
>> log-neighbor-changes Log neighbor up/down and reset reason
>> redistribute-internal Allow redistribution of iBGP into IGPs
>> (dangerous)
>> router-id Override configured router identifier
>> scan-time Configure background scanner interval
>>
>> R6(config-router)#bgp best ?
>> compare-routerid Compare router-id for identical EBGP paths
>> dampening Enable route-flap dampening
>> dmzlink-bw Use DMZ Link Bandwidth as weight for BGP multipaths
>> inject-map Routemap which specifies prefixes to inject
>> med MED attribute
>> scan-time Configure background scanner interval
>>
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