Pete
Thanks for your help. I know it doesnt buy much redundancy, however it is
something that could be done to an existing system without much capital
outlay, and the organisation that I was thinking of has seemed to have had
a run of bad luck with single routers falling over during the last few
months. I know the org would prefer to rely on the dual providers for
uplink redundancy rather than adding additional redundant links to any
single provider.
I dont even know if the upstream provider would allow it, but it was just
something that occured to me while reading up for the BGP exam I am taking
this week and I couldnt really find any answers in my study materials.
Yet again, thanks
Peter
--On 12 February 2003 16:28 +0000 Peter van Oene wrote:
> At 03:59 PM 2/12/2003 +0000, Peter Walker wrote:
>> Yep you are right.
>>
>> Lets try that again ...
>>
>> a) connect up1 to the same ethernet segment
>> b) form bgp neighbor relationship with BGP peer at provider pr2
>> c) advertise appropriate MED values requesting that pr2 prefer
>> up2
>> d) set local preference to prefer link via up2 to pr2 over
>> up1 to pr2
>>
>> In terms of what I am asking is, are there any issues with having two
>> 'redundant' bgp links from two different routers in one AS over a single
>> multi-access link to a single router in another AS.
>
> So basically you have two routers and both r1 and r2 connect to the same
> router on the provider side while r1 also maintains a connection to
> another router on the provider side. In this case, you don't really
> buy yourself much other than router redundancy on your side. The cost
> is purely in control traffic that will transit the ethernet link. BGP
> isn't that chatty unless peering sessions are flapping (which would be
> abnormal) so this shouldn't be a big problem. Only other cost would be
> additional config complexity which might impede troubleshooting. Beyond
> that, things should work fine as long as the provider agrees to set it
> up.
>
> Pete
>
>
>
>
>> It seems to me that this would be a simple no-brainer type of change to
>> make, but I just have a nagging suspicion that there is some gotcha
>> waiting to jump out when you least expect it. None of the sample
>> configurations I have seen seem to mention this sort of config and I was
>> wondering if there was some reason why it shouldnt be done, or if it was
>> just one of those obscure variations of common configurations that did
>> not warrant it's own explicit mention.
>>
>> Peter
>>
>> --On 12 February 2003 14:27 +0000 Peter van Oene wrote:
>>
>>> At 01:36 PM 2/12/2003 +0000, Peter Walker wrote:
>>>> Folks
>>>>
>>>> A quick question on external BGP connection configuration.
>>>>
>>>> Given an organisation (ORG) with 2 EBGP routers (up1, up2) and two
>>>> upstream providers (pr1, and pr2) where provider pr1 is currently
>>>> linked to the router up1 via a serial link and provider pr2 is
>>>> currently linked to router up2 via a traffic shaped and limited
>>>> ethernet link. ORG is does not allow transit between the providers.
>>>>
>>>> Is there any reason why ORG should not
>>>>
>>>> a) connect pr1 to the same ethernet segment
>>>> b) form bgp neighbor relationship with BGP peer at provider pr2
>>>> c) advertise appropriate MED values requesting that pr2 prefer
>>>> up2 d) set local preference to prefer link via up2 to pr2 over
>>>> up1 to
>>> pr2
>>>
>>>
>>> I'm not sure if you are messing up your prs and ups here, but I'm not
>>> following you entirely. Why would you not just peer both routers and use
>>> prepend/med and pref to control load like most folks do? Maybe
>>> explaining what is better or different about this approach would help
>>> explain what the approach is :)
>>>
>>> Pete
>>>
>>>
>>>
>>>
>>>
>>>> What I am looking for is technical (or business/political) reasons why
>>>> this is a good or bad idea.
>>>>
>>>> I understand that all this would give is redundancy at the router level
>>>> (up1, up2), the ethernet link and pr2's router are all still potential
>>>> single points of failure. I also understand that pr2 may not wish to
>>>> allow such a configuration.
>>>>
>>>> Also, what would need to be done to ensure that any changes made would
>>>> not have any impact on decisions regarding the routing choice between
>>>> pr1 and pr2?
>>>>
>>>> Regards
>>>>
>>>> Peter
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