From: Chris Lewis \(chrlewis\) (chrlewis@cisco.com)
Date: Mon Jun 27 2005 - 21:26:45 GMT-3
Ahh, it is clearer to me now.
So why does IOS let you configure this on sub-interface and not on main?
Not sure :)
What I believe is happening here though is that there is no internal
bridging. What is happening is when you ping 172.16.124.1, traffic is
load balanced out of S1/0.1 and S1/0.2 to the destinations at the other
end of the DLCIs, those routers then have a map statement (or are p2p
sub-interfaces) and can turn the packet around back towards the original
router. I believe it is just as normal for when you want a router to
ping a local IP on a frame interface, it sends the packet out where ever
the combination of routing table and frame map statements tell it to,
and as long as the remote end has a way of mapping it back, the ping
works.
Chris
-----Original Message-----
From: Pat Chui [mailto:cui666@gmail.com]
Sent: Monday, June 27, 2005 5:58 PM
To: Chris Lewis (chrlewis); Group Study
Subject: Re: same subnet IPs used on 2 different interfaces
Hi, Chris
I did in fact look at the routing table, and that's where I got
confused, R1 is the hub router and R2 and R4 are the spokes, I know R2
and R4 would see /32 for each of the p-t-p sub-interfaces on R1, but in
R1 I saw the following, it only generate /32 for the neighbor routers
but not itself, which is expected. it works perfectly fine.
But, just so I make my question clear, I was trying to understand how
the 2 sub-interfaces forward pkts btw them, or in another word, why IOS
allows this type of configuration on 2 subinterfaces but not on 2
physical interfaces?
Thanks,
Pat
===
R1#sh ip route 172.16.124.1
Routing entry for 172.16.124.0/24
Known via "connected", distance 0, metric 0 (connected, via interface)
Redistributing via eigrp 1, ospf 1, rip
Advertised by eigrp 1
rip
Routing Descriptor Blocks:
* directly connected, via Serial1/0.1
Route metric is 0, traffic share count is 1
directly connected, via Serial1/0.2
Route metric is 0, traffic share count is 1
R1#sh ip route 172.16.124.2
Routing entry for 172.16.124.0/24
Known via "connected", distance 0, metric 0 (connected, via interface)
Redistributing via eigrp 1, ospf 1, rip
Advertised by eigrp 1
rip
Routing Descriptor Blocks:
* directly connected, via Serial1/0.1
Route metric is 0, traffic share count is 1
directly connected, via Serial1/0.2
Route metric is 0, traffic share count is 1 R1#sh ip route
172.16.124.4 Routing entry for 172.16.124.4/32
Known via "ospf 1", distance 110, metric 64, type intra area
Redistributing via eigrp 1, rip
Last update from 172.16.124.4 on Serial1/0.1, 00:07:07 ago
Routing Descriptor Blocks:
* 172.16.124.4, from 172.16.124.4, 00:07:07 ago, via Serial1/0.1
Route metric is 64, traffic share count is 1
R1#sh ip route 172.16.124.5
Routing entry for 172.16.124.5/32
Known via "ospf 1", distance 110, metric 64, type intra area
Redistributing via eigrp 1, rip
Last update from 172.16.124.5 on Serial1/0.2, 00:07:10 ago
Routing Descriptor Blocks:
* 172.16.124.5, from 172.16.124.5, 00:07:10 ago, via Serial1/0.2
Route metric is 64, traffic share count is 1 On 6/27/05, Chris
Lewis (chrlewis) <chrlewis@cisco.com> wrote:
> Have you looked at the routing table and seen what effect the OSPF
> network type has on that?
>
> Chris
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of Pat Chui
> Sent: Monday, June 27, 2005 12:48 PM
> To: Group Study
> Subject: same subnet IPs used on 2 different interfaces
>
> Guys,
> I had this scenario in which I have to get 2 FR p-t-p sub-interfaces
> to use IPs on the same subnet in one router, and it's pingable between
> the
> 2 sub-interfaces. I was wondering if any sort of bridging mechanism
> enabled auto-magically or else? Maybe you can help me to understand
> this.
>
> Thanks,
> Pat
>
> ======
> interface Serial1/0.1 point-to-point
> ip address 172.16.124.1 255.255.255.0
> ip ospf network point-to-multipoint
> frame-relay interface-dlci 104
> !
> interface Serial1/0.2 point-to-point
> ip address 172.16.124.2 255.255.255.0
> ip ospf network point-to-multipoint
> frame-relay interface-dlci 102
> !
>
> ======
> R1#ping ip
> Target IP address: 172.16.124.1
> Repeat count [5]:
> Datagram size [100]:
> Timeout in seconds [2]:
> Extended commands [n]: y
> Source address or interface: 172.16.124.2 Type of service [0]:
> Set DF bit in IP header? [no]:
> Validate reply data? [no]:
> Data pattern [0xABCD]:
> Loose, Strict, Record, Timestamp, Verbose[none]:
> Sweep range of sizes [n]:
> Type escape sequence to abort.
> Sending 5, 100-byte ICMP Echos to 172.16.124.1, timeout is 2 seconds:
> Packet sent with a source address of 172.16.124.2 !!!!!
> ======
>
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