From: Brian McGahan (bmcgahan@internetworkexpert.com)
Date: Fri May 27 2005 - 13:50:19 GMT-3
What lab and task is this from?
Brian McGahan, CCIE #8593
bmcgahan@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
> >>
> >>
This archive was generated by hypermail 2.1.4 : Fri Jun 03 2005 - 10:12:03 GMT-3