From: John Conzone (jkconzone@xxxxxxxx)
Date: Sat Aug 05 2000 - 12:49:28 GMT-3
I've started at a new job and am familiarizing myself with the
network. We have a large BPX/MGX backbone which we use to provide ISP
service, but our coporate LAN/WAN utilizes the backbone services as
well.
I was looking at the LAN in our local office and noted that there
is a CAT 5000 with a rsp running VLAN interfaces for each local
subnet. The Cat has a LANE mod and tS1010 in the same chassio. The
default gateway for the local LAN is a virtual subinterface on a MGX
RSM.
Here's my question. VLAN 100 on the CAT 5 (int VLAN100, ip
192.168.201.2) is bound to a pvc (0/32) on the LANE mod (atm pvc bind
command). The lane mod bridges through the backplane to the LS1010,
where pvc 0/32 is switched out another LS1010 port to the BPX as pvc
0/702, and then switched to the MGX as 0/702, which is then mapped to
a virtual subinterface on the MGX router blade.
What I noted is that on the MGX router blade, the virtual
subinterface has no ip address. Instead it has a bridge group
assigned, and then IRB is enabled. The ip address 192.168.201.1 is
assigend to the BVI. No other interfaces on the MGX RSM are in this
bride group. Bridge 1 is routing IP.
I asked the guy who set this up why and he said that it wouldn't
work if the ip was assigned on the MGX RSM subinterface directly. He
doesn't remember why but says it wouldn't work any other way.
Not having a lot of production hands on with ATM yet (thats why I
took the job!) I can't figure out why the IRB. If we're not bridging
with any other interfaces, why not route rght on the sub?
Any ideas?
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