Information Technology Reference
In-Depth Information
Table14-1 XNS: Clients Cannot Connect to Servers over Router (continued)
Possible Problem
Solution
Backdoor bridge
between segments
Use the
show xns traffic exec
command to determine
whether the bad hop count field is incrementing. The XNS
network updates by default occur every 30 seconds:
1.
C4000#show xns traffic
Rec: 3968 total, 0 format errors, 0 checksum errors,
0 bad hop count,
3968 local destination, 0 multicast
[...]
2.
If this counter is increasing, use a network analyzer to look
for packet loops on suspect segments. Look for routing
updates. If a backdoor bridge exists, you will probably see
hop counts that increment up to 15, at which point the route
disappears. The route reappears unpredictably.
3.
Use a network analyzer to examine the traffic on each
segment. Look for known remote network numbers that
appear on the local network. That is, look for packets from a
remote network whose source address is not the source
address of the router.
The backdoor is located on the segment on which a packet from
a remote network appears whose source address is not the source
address of a local router. To prevent XNS routing updates from
being learned from the interface connected to the same segment
as the backdoor bridge, you can use the
xns
input-network-filter
command.
Example:
In the following example,
access list 476
controls which
networks are added to the routing table when RIP packets are
received on Ethernet interface 1. Network 16 is the only network
whose information will be added to the routing table. Routing
updates for all other networks are implicitly denied and are not
added to the routing table:
access-list 476 permit 16
interface ethernet 1
xns input-network-filter 476
1.
RIP = Routing Information Protocol
XNS: XNS Broadcast Packets Not Forwarded by Router
Symptom:
XNS servers do not respond to broadcast requests from clients.
