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Aironet 1200 networking setup issue

 
 
Claudiu
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      04-19-2005
Hello,

I deployed a wireless network between our University's buildings. As
access point, I used a Cisco Aironet 1200 with 802.11b/g radio module.

The setup is somehow like this:

Internet -> Router <- LAN -> Router2 <-(- ... AP ... -) Client 1, 2, 3,
...., N

The client wireless equipment is Cisco's Linksys WET 11 v2 (802.11b).
The AP is configured as AP root, has the ethernet interface not used. I
choose this deployment because I have no technical solution to go with
a LAN link in AP's place. Router2 is a Linux 2.6.x box. Router2 has no
filters, ip forwarding enabled, all policies set to ACCEPT (no
firewall).

On the ethernet ports of Client 1,2,3... are routers (linux boxes)
also, that provides NAT and do traffic separation, firewall filtering
etc.

Client X's and Router2 interface from the AP side have IP addresses s
in the same IP subclass (a /28 block). This setup has the following
problem:
- if from Client X's linux box ping Router2, it respond.
- (1) if from Client X's linux box ping an IP from LAN, doesn't
responds. (LAN have different IP subclass - a /26 block)
- (2) if from a LAN computer ping the Client X's box, it responds and
from now on the Client X's ping in that LAN IP works.
- (1) and (2) is the same with any IP from the Internet, also - I
tested with some other servers where I have access to.

Ok. Now, I gone deeper into the problem. A tcpdump session on the
Clinet X's linux box shows the IP packets with correct source IP,
correct destination IP, and the MAC addresses of the frame: src: the
linux box source MAC, destination Router2 "to AP" interface MAC:

turbo:~# tcpdump -i eth1 -qtennl icmp
tcpdump: verbose output suppressed, use -v or -vv for full protocol
decode
listening on eth1, link-type EN10MB (Ethernet), capture size 96 bytes
00:48:54:6d:49:51 > 00:02:b3:b2:12:ed, IPv4, length 98: IP X.X.X.244 >
193.0.0.193: icmp 64: echo request seq 1708

On the "to AP" ethernet interface of the Router2, comes:
00:48:54:6d:49:51 > ff:ff:ff:ff:ff:ff, IPv4, length 98: IP X.X.X.244 >
193.0.0.193: icmp 64: echo request seq 1708

So, the frame comes with the destination MAC changed into
FFFF.FFFF.FFFF (broadcast MAC).

The Cisco Aironet 1200 is configured in IRB Bridging mode - built in,
can't be changed. Uses IOS software version 12.2 (13) JA4 (I see from
the image: c1200-k9w7-mx.122-13.JA4) The dot11 interface and fast
ethernet interface are in the bridge-group 1

What I assume is:
The cisco checks the packets/frames in routing mode, sees the
destination to not known IP address (not associated) and changes the
MAC to broadcast. If one packet comes from outside, learns the source
IP and the communication goes well. Anyway, sometime it starts to work
well to all the internet destinations.

What is wrong with it? Also, I assigned one IP from Router2 and
client's IP block to the AP on bvi1 interface and uses ip
default-gateway to set the gateway to Router2. No result. I just want
that packets to flow trough the AP and no routing decision to be made.
If not possible, how to configure it to work in my desired deployment?

 
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