From: Brian McGahan (bmcgahan@internetworkexpert.com)
Date: Fri Jun 27 2008 - 14:30:33 ART
Hi Mohamed,
The BGP router-id comes from the highest loopback address, or if
there is no loopback, your highest interface IP address. The cluster-id
comes from the router-id. In a real design you would always want to
hard code at least the BGP router-id, and possibly the cluster-id
depending on the design. There are certain designs that if your BGP
router-id overlaps with someone else's there could be a problem, such as
if you're doing Anycast RP for multicast. As a general rule OSPF,
EIGRP, and BGP router-id's should always be hardcoded. In the lab exam
if there isn't a requirement *not* to hardcode them, you should set it
to a unique IP address configured on the router.
HTH,
Brian McGahan, CCIE #8593 (R&S/SP/Security)
bmcgahan@internetworkexpert.com <mailto:bmcgahan@internetworkexpert.com>
Internetwork Expert, Inc.
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Net Plus wrote:
> Hi Brian,
>
> It means;
>
> Once you set the bgp Router-id, You don't need any Cluster-id, As per your
> statement, bgp cluster-id is derived from Router-id.
>
> Regards,
>
> Mohamed.
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> Brian McGahan
> Sent: Friday, June 27, 2008 9:55 AM
> To: cciestruggle; Cisco certification
> Subject: Re: the relation between the route-reflector servers within the
> same bgp cluster id?
>
>
> You should statically set the BGP router ID to a globally significant
> address on the router. The cluster-ID is inherited from router-id
> regardless if you hardcode it or the router-id though.
>
> Brian McGahan, CCIE #8593 (R&S/SP/Security)
> bmcgahan@internetworkexpert.com <mailto:bmcgahan@internetworkexpert.com>
>
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com
> Toll Free: 877-224-8987 x 705
> Outside US: 775-826-4344 x 705
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>
> cciestruggle wrote:
>
>> Hello Brain,
>>
>> We do need to have the cluster id on the router reflectors to avoid
>> loops ? right?
>>
>> And further more do we need to explicitly specify the cluster id? the
>> command reference says that it is automatically set to the local
>> router id (of which reflector ?)
>>
>>
>>
> http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_bgp1.html#
> wp1012377
>
>> Zealot
>>
>> On Fri, Jun 27, 2008 at 3:52 PM, Brian McGahan
>> <bmcgahan@internetworkexpert.com
>> <mailto:bmcgahan@internetworkexpert.com>> wrote:
>>
>> You can, but you don't necessarily have to. Most large scale route
>> reflection designs include a full mesh of peerings between
>> clusters via
>> the route reflectors, but the route reflectors are not clients of each
>> other. This means that if reflector A peers with reflector B, and
>> reflector B peers with reflector C, reflector C cannot learn a route
>> from reflector A's cluster through B's cluster, because if A is a
>> non-client of B, B cannot advertise an iBGP route from A to C.
>> However
>> if these is a full mesh of non-client iBGP peerings between A, B,
>> and C,
>> reflector C wouldn't need to use B to get to A, since it has a direct
>> peering.
>>
>> Ultimately for production it depends on your redundancy design.
>> Technically you can have every single router be a router reflector
>> with
>> everyone else beings its clients. You won't cause any routing loops,
>> since the cluster list prevents this, but instead you'll just have
>> a lot
>> of unnecessary route replication. However when we are talking about
>> update messages in the order of 300,000 routes for the full BGP table,
>> scalability from a resource management perspective is highly
>> affected by
>> route reflection design.
>>
>>
>> HTH,
>>
>> Brian McGahan, CCIE #8593 (R&S/SP/Security)
>> bmcgahan@internetworkexpert.com
>> <mailto:bmcgahan@internetworkexpert.com>
>> <mailto:bmcgahan@internetworkexpert.com
>> <mailto:bmcgahan@internetworkexpert.com>>
>>
>> Internetwork Expert, Inc.
>> http://www.InternetworkExpert.com
>> Toll Free: 877-224-8987 x 705
>> Outside US: 775-826-4344 x 705
>> 24/7 Support: http://forum.internetworkexpert.com
>> Live Chat: http://www.internetworkexpert.com/chat/
>>
>>
>> ccie wrote:
>> > Hi experts,
>> >
>> > Assume I have 5 router within the same AS, and two of them will
>> have IBGP
>> > peer with the rest, So I configure these two with the same bgp
>> cluster-id,
>> > and configure the rest to be their route-reflector-clients. Should I
>> > configure these two to be route-reflector-clients to each others!!!
>> >
>> > Thanks in advance
>> >
>> > Amin
>> >
>> >
>> >
>>
>>
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