From: Sean C (Upp_and_Upp@hotmail.com)
Date: Fri May 27 2005 - 15:27:45 GMT-3
Tim mentioned it came from IE Vol 2, Lab 6. Not sure of the tasks but I
think it was tasks 5.36-5.38. I think the router names may have changed.
----- Original Message -----
From: "Brian McGahan" <bmcgahan@internetworkexpert.com>
To: "ccie2be" <ccie2be@nyc.rr.com>; "Mark Lasarko" <mlasarko@co.ba.md.us>;
"GroupStudy" <ccielab@groupstudy.com>
Sent: Friday, May 27, 2005 12:50 PM
Subject: RE: BGP Load-balancing paths
> What lab and task is this from?
>
> Brian McGahan, CCIE #8593
> bmcgahan@internetworkexpert.com
>
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com
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>
>> -----Original Message-----
>> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
>> ccie2be
>> Sent: Friday, May 27, 2005 10:53 AM
>> To: 'Mark Lasarko'; 'GroupStudy'
>> Subject: RE: BGP Load-balancing paths
>>
>> 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
> /1
>> 22
>> 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_note09186a008009
> 41
>> 95
>> > .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/
> ip
>> rr
>> > 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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