Layer 3 switch with AT&T Metro Ethernet

Unanswered Question
Giuseppe Larosa Mon, 03/23/2009 - 05:55

Hello Jose,

you need to take some design decisions:

are you going to use a dynamic routing protocol on the metro ethernet links to be able to detect remote end failure ?

example with OSPF:

assign two IP subnets one to each Metro ethernet link

metro E link1:

metro E link2:

client vlan with ASA:

internal client vlans behind ASA:

router ospf 10

network area 0

network area 0

network area 0

the ASA can talk OSPF too or it can use static default route

in any case some device, the ASA or the L3 switch needs to advertise in OSPF the client/server vlans behind the ASA.

if it the ASA and the ip subnets are connected you can use the network area command

if you decide to use static routes between the ASA and the L3 switch the L3 switch has to redistribute the static routes in OSPF

router ospf 10

red static subnets

note: OSPF automatically load balances and perform fail-over over up to 4 paths.

on the remote site devices at the other ends of the metro ethernet links you should do the same using the same commands

Hope to help


Giuseppe Larosa Mon, 03/23/2009 - 06:32

Hello Jose,

usually metro ethernet links are seen as L2 services if this is not the case my previuos post is useless.

so you have two internet links with public ip addresses you need to think to some form of tunneling to avoid to expose your internal traffic

Hope to help


Giuseppe Larosa Wed, 03/25/2009 - 08:04

Hello Jose,

the configuration of my first post should apply to your scenario.

you need an IOS that allows to use a routing protocol on c3750

OSPF and BGP requires ip services image:

IP routing protocols for load balancing and for constructing scalable, routed backbones:

-RIP Versions 1 and 2

>> -OSPF (requires the IP services image)

-Enhanced Interior Gateway Routing Protocol (EIGRP) IPv6 to utilize IPv6 transport, communicate with IPv6 peers, and advertise IPv6 routes

-Border Gateway Protocol (BGP) Version 4 (requires the IP services image)


modular QoS is supported.

Hope to help



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