From: Sean C (Upp_and_Upp@hotmail.com)
Date: Fri May 27 2005 - 11:50:52 GMT-3
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/122t/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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