Re: MPLS EIGRP backdoor links - SoO

As a side note, EIGRP SoO is a legacy feature that's not needed anymore, because the EIGRP Cost Community encodes the individual vectors of the composite metric calculation into BGP. This way the remote sites run a normal feasibility condition against the end to end path, and it's not possible to cause a loop between sites.

SoO isn't needed unless you're running old code that doesn't support Cost Community. It's possible you could get tested on it in the lab but it's not a practical problem anymore.

Brian McGahan, CCIE #8593 (R&S/SP/Security)
bmcgahan_at_INE.com

Internetwork Expert, Inc.
http://www.INE.com

On Nov 1, 2011, at 5:22 PM, "Jochen Bartl" <jochen.bartl_at_gmail.com> wrote:

> Since Paul has already mentioned that you can verify the SoO value
> with "show ip eigrp topology XXXX", I would like to throw in some
> additional info here. I`ve built a mini lab because I wanted to know
> in detail how EIGRP carries the SoO value across the backdoor link.
>
> After capturing some packets[1] on the backdoor link I could find out
> that EIGRP is using the TLV type 260 for SoO. The data inside the TLV
> looks something like this.
>
> 01 04 -> TLV Type (260)
> 00 14 -> TLV Length: 20 bytes
> 0a 00 19 00 -> TLV references IP routing TLV with route 10.0.25.0
> 00 00 00 -> Not sure yet?
> 08 -> Ext Community Lengh? 8 bytes
> 00 03 -> Ext Community Type?
> 00 64 00 00 00 02 -> SOO Ext communit value: 100:2
>
> I haven't figured out all the header fields yet, but I could at least
> identify the SoO value of 100:2 in the last 6 bytes of the TLV. The
> hex data is from packet 38 in the capture file[1]. Wireshark/Scapy
> doesn't decode the TLV at the moment, but I promise to write a patch
> as soon as I've identified all the header fields correctly ;-)
>
> Petr Lapukhov has also written a great document about EIGRP SoO:
> http://blog.ine.com/2010/04/29/understanding-eigrp-soo-and-bgp-cost-community/
>
> Best regards,
>
> Jochen
>
>
> 1) http://www.cloudshark.org/captures/327a223fadf3
>
> On Tue, Nov 1, 2011 at 8:14 PM, Tom Kacprzynski <tom.kac_at_gmail.com> wrote:
>> Hello,
>> I'm working on a lab using EIGRP as the protocol for MPLS VPN. This
>> scenario has a backdoor link. I'm testing the Site of Origin feature, but
>> can't seem to find any way to check the actual SoO on the CE router using
>> EIGRP commands. Does anyone know how/if I could do that?
>>
>> I can see it in BGP table but how do I see it in EIGRP
>>
>> Rack1R6#sh ip bgp vpnv4 rd 100:1 155.1.67.0/24
>> BGP routing table entry for 100:1:155.1.67.0/24, version 338
>> Paths: (1 available, best #1, table VPN-A)
>> Advertised to update-groups:
>> 1
>> Local
>> 0.0.0.0 from 0.0.0.0 (150.1.6.6)
>> Origin incomplete, metric 0, localpref 100, weight 32768, valid,
>> sourced, best
>> Extended Community: SoO:100:60 RT:100:1
>> Cost:pre-bestpath:128:28160 <----------------------
>> 0x8800:32768:0 0x8801:10:2560 0x8802:65280:25600 0x8803:65281:1500
>> mpls labels in/out 22/nolabel(VPN-A)
>>
>>
>>
>> Thank you,
>>
>> Tom
>>
>>
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Received on Tue Nov 01 2011 - 21:20:13 ART