From: Rick Burts (burts@xxxxxxxxxxxxxx)
Date: Tue Sep 05 2000 - 03:29:24 GMT-3
John
Your situation makes much more sense after you explained more about
your topology. On R2 Serial you are doing encapsulated bridging:
the router receives an Ethernet (IPX) frame which it wants to forward
to R3 and so it encapsulates the Ethernet frame with the serial header
(HDLC or whatever). If R2 were routing, it would have stripped off the
Ethernet header and encapsulated the IPX layer 3 data in the serial
header. The crucial difference is whether in the serial frame the
payload is an Ethernet frame or layer 3 IPX.
When R3 is routing on Serial, it receives the frame and looks at the
payload and is not sure what to do with the Ethernet frame. When R3 is
bridging (and using BVI) the serial receives the frame (doing
encapsulated bridging) and knows to strip the serial header and pass
the payload to the BVI which correctly knows how to process the data.
Rick
On Mon, 4 Sep 2000, John Conzone wrote:
>
> ----- Original Message -----=20
> From: John Conzone=20
> To: kkriel@netscape.net ; :ccielab@groupstudy.com=20
> Sent: Monday, September 04, 2000 10:17 AM
> Subject: Re: routed versus bridged interface
>
>
> Hi, Kenny. I understand that.
> What I am looking to do is break down the packets and go over =
> exactly what is happening.
> If R1 is routing IPX , he looks in his routing table and see's IPX =
> network 700 on E0. Good. So the packet goes out on R1 E0.
> R1 E0 is attached to R2 E0, which isn't routing IPX, but is in =
> bridge group 1. So R2 E0 bridges the packet. Okay. R2 has another =
> interface, Serial 0, which is in the same bridge group and isn't routing =
> IPX. Good so R2 E0 bridges the packet over to R2 S0, which send it out =
> its interface.
> So far so good?
> Okay. R2's S0 is directly attached to R3's S1. R3's S1is routing IPX =
> and is on the same network, 700. He gets the packet that was bridged =
> over from R2. It would sem to me that the bridged network in between the =
> routed interfaces shouldbe transparent to them.=20
> I know i'm missing something. Is it the ethernet to serial =
> conversion?
> =20
> ----- Original Message -----=20
> From: Kenneth Kriel=20
> To: John Conzone=20
> Sent: Monday, September 04, 2000 12:34 PM
> Subject: RE: routed versus bridged interface
>
>
>
> John,
>
> If you have routing and bridging enabled on an interface then it will =
> route the frame and not bridge it. The rule is : when a router receives =
> a frame - check if it is routable, if so pass it to the routing engine, =
> if it is not then, and only then, bridge it.
>
> That is why it is working with IRB !
>
> Hope this helps !
>
> Ken
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf =
> Of John Conzone
> Sent: Sunday, September 03, 2000 11:14 PM
> To: ccielab
> Subject: routed versus bridged interface
>
>
> Guys, help me out again. Here's the scenario. I have three =
> routers in a row.
>
> R1-----------R2------------R3
>
> On R1, I'm routing IPX on its interface connected to R2, as well =
> as running bridging.
> On R2, I only have bridging on both interfaces. No ipx routing.
> On R3, I have IPX routing turned on onthe interface connected to =
> R2, and also bridging.
>
> I cannot ping IPX bewteen R1 and R3. They are the same IPX =
> network.=20
> If I configure IRB on R3, remove the IPX network from R3's =
> interface, put it on the BVI on R3 and route IPX on the BVI and it =
> works. The packets must be getting to R3 either way, but R3 cannot =
> decapsulate them when routing directly on the interface becasue he is =
> looking for a "routed" packet, but is recieveing a "bridged" packet from =
> R2.
> Moving the IPX routing off the interface onto the BVI allows the =
> "bridged"packet to be decapsulated and passed to the BVI as a "routed" =
> packet.
> Can someone break out what the packet looks like coming out of =
> R1, then out of R2 into R3?
> What is it specifically in the packet header , the "bridged" =
> packet, that R3 see's when he tries to "route" the packet, that he =
> doesn't like. I'm drawing a blank although in my gut I understand whats =
> happening.
> I've run into this when binding a virtual interface on a RSP on =
> a cat to a lane card, and then sending it to a router. I had to use BVI =
> to get the 1483 "bridged" packet to route.
> =20
>
> =20
>
>
Rick Burts, CCSI CCIE 4615 burts@mentortech.com
Mentor Technologies 410-280-8840 ex 3015
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