From: Daniel Kutchin (daniel@kutchin.com)
Date: Tue Oct 21 2008 - 14:23:15 ARST
What does the "rcvd 3" mean in "debug ip packets"?
*Mar 1 01:34:55.127: IP: tableid=0, s=102.1.1.1 (local), d=101.1.1.1
(FastEthernet0/0), routed via FIB
*Mar 1 01:34:55.127: IP: s=102.1.1.1 (local), d=101.1.1.1
(FastEthernet0/0), len 100, sending
*Mar 1 01:34:55.127: ICMP type=8, code=0
*Mar 1 01:34:55.127: IP: tableid=0, s=101.1.1.1 (FastEthernet0/0),
d=102.1.1.1 (FastEthernet0/0), routed via RIB
*Mar 1 01:34:55.127: IP: s=101.1.1.1 (FastEthernet0/0), d=102.1.1.1
(FastEthernet0/0), len 100, rcvd 3 <---
*Mar 1 01:34:55.127: ICMP type=0, code=0
Oh, the simple things...
Daniel
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Huan
Pham
Sent: Dienstag, 21. Oktober 2008 09:03
To: Marko Milivojevic; GS CCIE-Lab
Cc: Raheel Itrat
Subject: RE: diffrent Subnet IPs on same VLAN and Proxy-Arp
Hi Raheel,
Marko's soluton are surely valid options.
In addition to static ARP, and mobile IP, we can also disable routing
all together on both routers, or you can have a secondary IP of each
other subnet, and they should be able to ping each other. No need any
static route for both cases, obviously, as when you disable routing the
routers will only act like hosts, without routing functionality. When
you have the secondary IP configure, the routers have the route to each
other already.
I would just like to add some input as to why these are needed.
By default, when routing is enabled, routers will not respond to arp
requests from stations whose source IP addresses are not on the IP
subnet that receives the request, regardless of whether proxy arp or
local proxy arp is enabled or not.
When R1 try to ARP for R2 IP address, R2 will see the ARP comes from
101.1.1.1 on the interface that has IP of 102.1.1.1/24, and will ignore
it.
R2#
*Mar 1 06:39:11.166: IP ARP req filtered src 101.1.1.1 0000.1111.1111,
dst 101.1.1.2 0000.0000.0000 wrong cable, interface FastEthernet0/0
To disable this sanity check, you will have to use any of the three
solutions above
1. Static ARP
R2#
arp 101.1.1.1 0000.1111.1111 arpa
2. Local LAN Mobility
R2#
interface FastEthernet0/0
mac-address 0000.2222.2222
ip address 102.1.1.1 255.255.255.0
ip mobile arp
See the debug message that R2 now does not complain any more about ARP
from wrong subnet!
R2#
*Mar 1 06:43:15.334: IP ARP: rcvd req src 101.1.1.1 0000.1111.1111, dst
102.1.1.1 FastEthernet0/0
*Mar 1 06:43:15.334: IP ARP: sent rep src 102.1.1.1 0000.2222.2222,
dst 101.1.1.1 0000.1111.1111 FastEthernet0/0
3. Disable routing on both routers.
4. Configure secondary IP address.
The Local Proxy Arp or Proxy Arp are not required here.
- Local proxy arp is used, so that a router can work as proxy for two
hosts on the same subnet, which normally can not communicate directly
(e.g. Private VLAN or on protected port).
- Proxy arp (on by default) is used so that router responds on any ARP
for subnets outside LAN subnet (e.g. when you have a default static
route on R1 pointing to e0/0, instead of R2 LAN IP, you will need to
enable R2 proxy arp (on by default).
As said above, both these options does not work for you, because you
have a different IP subnet on the two routers, and by default, routers
just ignore ARP request from each other.
Hope this helps,
Blogs and organic groups at http://www.ccie.net
This archive was generated by hypermail 2.1.4 : Sat Nov 01 2008 - 15:35:21 ARST