Unanswered Question
Apr 12th, 2007
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the layout is as follows:

6509(data center)-->3845---->MPLS ISP cloud--->3845(remote site)--->stacked 3750

we would like to extend few vlans to the remote site. i am planning to trunk vlans to the router and use xconnect on the subinterfaces on the two 3845s.

ISP is going to give us a ospf handoff ( so ospf CE-PE vrf). i have been doing some research (i have deployed EoMPLS across two data centers on the 6500s via loopback cable( port-based xconnects)) and since

i cannot do MPLS with the provider as the provider is only going to give me routes via vrf i have to find another way of establishing MPLS label switching with the remote site - GRE over MPLS seems to be the option

i would appreciate if you could shed some light on this as how would it work??

Also i can do targeted ldp with the remote site router without enabling tag-switching on the CE egress interfaces - does this mean that i could send packets to ISP with my labels and the provider will switch my traffic

with its own lables stacked on top of the my lable where my origianl lable is preserved and it gets to the remote site. here is my understanding correct - or i have lost it compelety...


with GRE what kind of mtu sizes am i looking at

ethernet header 14

GRE header ?

MPLS labels 8-20

EoMPLS header 4

original 802.1q frame 4

appreciate any input


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jiangu Sun, 04/15/2007 - 23:10
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I think your only option is run L2TPv3 between two 3845s.

uchaudhry Mon, 04/16/2007 - 06:05
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thanks for the reply - yeah i think so too. For future multicast needs i am thinking of using MPLS over GRE (or i can use l2tpv3 and a GRE tunnel only for multicast).

i think the determining factor would be the MTU size.

Question: how can i get around the MTU issue - L2tpv3 adds around 16~20 bytes or if i use GRE over MPLS to deploy EoMPLS i could add up to 70 bytes...

jiangu Mon, 04/16/2007 - 09:25
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I just tried on my setup, it works like a charm.

I guess you were thinking about (Eo)MPLS-over-GRE-over (L3) MPLS (VPN), I did not try it, but I doubt it will work.

uchaudhry Mon, 04/16/2007 - 10:11
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what did you try? l2TPv3 or MPLS over GRE??

If MPLS over GRE: please forward the config...




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