From: Geatti (geatti@xxxxxxxx)
Date: Sun Sep 17 2000 - 11:09:51 GMT-3
This is very interesting John. Never tried it myself. You say that IRB
works but regular transparent doesn't. My understanding is that with
IRB all protocols are bridged by default. With regular transparent all
are bridge except IP. So it may be possible that even though you are
pinging the router (R4) is trying to route not bridge, and as you have
no ip addresses on your isl interfaces it can't route to your subnet.
I would TURN OFF ip routing (no ip routing) and see if it works then,
the router should now bridge ip rather than attempting to route it.
Again I haven't tried this so this is an educated guess. Let us know
if you fix it as I'd be interested in what works.
Marco ...Lab in 3 days, aaaaahhhhhhhhhhhhh.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
John Conzone
Sent: Saturday, September 16, 2000 6:26 PM
To: ccielab
Subject: bridging vlan on ISL trunk
First, before anyone says why are you doing this, I'm doing this
because this is the twisted stuff that I might see on the lab. Now for
the question.
I have three routers connected to a Cat5 as such.
R4
|
|
R3---------------CAT5----------------R5
R3 has ethernet into a port on Cat in VLAN 1. R5 has ethernet into
a port on Cat in VLAN 2. Both in same ip subnet , 192.168.10.3 and
192.168.10.5.
R4 is connected via ISL trunk to Cat. R4 has subint fa0/0.1 encap
ISL 1 and subint fa0/0.2 encap isl 2.
Now I have no ip on either subint on R4. I create bridge group 1
on R4, and place both sub interfaces in the bridge group. I try to
ping betwen R3 and R5 with no luck. I then create BVI, put it in
subnet, route IP on bridge group and R3 and R5 can ping.
I need someone to tell me if what I think is happenig when it
fails without IRB is what is really happening, or if not what is
happening. I'm thinking the reason the pings fail without the bvi is
that R3 sends a packet out to the Cat. Say its an arp (cause it is, I
debugged it). The packet gets to the Cat, gets encapsulated in ISL1 to
go up the trunk to R4.
R4 is bridging bewteen the subs, so he takes the packet bridges it
over to fa0/0.2, encapsulates it again in ISL 2 and sends it down
fa0/0.2 towards the cat and vlan 2. So now I'm thinking I have a
packet with 2 ISL headers. The packet goes back down the trunk to the
Cat to VLAN 2. The cat strips off the outermost ISL header (isl2) and
forwards the packet to R5 with the ISL1 header still on it. R5 gets a
ISL encap packet and doesn't know what to do with this. Or perhaps
becasuse the packet isn't an etehrnet packet headin out the etehrnet
port, the Cat drops it.
When I use a BVI on R4, he strips the fist ISL header, so when the
packet reaches R5, it is a ethernet packet with no ISL header.
Of course this could be totally wrong, but it sounds good! Someone
let me know if I'm wrong. (As if I have to ask that with this
bunch!<G>)
John
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