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Webcast-Catalyst9k
New Member

Switch mac-address-table not populating

Hello all,

I have a very weird issue at the moment is a Cisco 887 DSL router running IOS Version 15.2(4)M6.

The IP address of a LAN device appears in the router arp cache but does NOT appear in the switch mac-address-table

Even if you ping the end device, get a response and then immediately check the mac-address-table there is no sign of it.

How is this possible? Surely as soon as the device sends a single frame into the switch port (and we're getting ping responses) the table should be populated.

Even more curious is the fact that the above holds true if you send one lot of pings (5 being the standard), it holds if you set the repeat to 100 BUT if you send 1000 pings to the device all of a sudden the mac-address appears!

I've replicated this issue several times and it's always the same.

At first I thought maybe the mac-address-table timeout value was really low and I just wasn't able to run the command quickly enough to see it in there but I've checked this and it's set to the default of 300.

Can anyone shed some light on this please?

Many thanks,

Luke

 

Everyone's tags (3)
4 REPLIES
New Member

What is the LAN device? and

What is the LAN device? and how did you verify it was in the arp cache? did you issue a "sho ip arp"? and when you say it is not in the cam table is this because you issued a "show mac-address-table".

 

The device you have is a layer 2 (built in switch module) and a layer 3 device (router). if you are not using the layer 2 functionality of the device...ie its a point to point link (l3 only) then the built in switch will  not have a mac address for it in the cam table. does the "show vlan-switch"  command work and if so what is the output?

New Member

Hi Jeffery,thanks for your

Hi Jeffery,

thanks for your input.

The LAN device is an IP-handset. I believe it's a Cisco 525.

Yes, I issued a show ip arp (well, show arp - Got the same result from both) and yes I am using show mac-address-table to check the CAM table.

The LAN is configured as a /24 private network with all the switch-ports on the device configured as access-ports in that network - No P2P links.

As requested, here is the output of the show vlan-switch command

 

BMT-45959#show vlan-switch

VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
1    default                          active    Fa0, Fa1, Fa2, Fa3
1002 fddi-default                     act/unsup
1003 token-ring-default               act/unsup
1004 fddinet-default                  act/unsup
1005 trnet-default                    act/unsup

VLAN Type  SAID       MTU   Parent RingNo BridgeNo Stp  BrdgMode Trans1 Trans2
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------
1    enet  100001     1500  -      -      -        -    -        1002   1003
1002 fddi  101002     1500  -      -      -        -    -        1      1003
1003 tr    101003     1500  1005   0      -        -    srb      1      1002
1004 fdnet 101004     1500  -      -      1        ibm  -        0      0   
1005 trnet 101005     1500  -      -      1        ibm  -        0      0  

New Member

ping x.x.x.xshow ip arp x.x.x

ping x.x.x.x
show ip arp x.x.x.x
show mac-address-table for MAC received from command above.

Keep in mind the the outgoing port could be a trunk port, so you can use the show cdp neighbor <interface name> detail to get the management IP address of the device

New Member

Ok, I don't know if you're

Ok, I don't know if you're asking me to run those specific commands on the device and post the output? At any rate, those are the commands I've been running to get to this point but here's the output anyway.

BMT-45959#ping 192.168.1.65
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.65, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/4 ms
BMT-45959#show ip arp 192.168.1.65
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  192.168.1.65            3   e8ed.f36a.6310  ARPA   Vlan1
BMT-45959#show mac-ad
BMT-45959#show mac-address-table
Destination Address  Address Type  VLAN  Destination Port
-------------------  ------------  ----  --------------------
b838.61ac.ecfa          Self          1     Vlan1
e8ed.f36a.5fd7          Dynamic       1     FastEthernet1

BMT-45959#ping 192.168.1.65
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.65, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/4 ms
BMT-45959#show ip arp 192.168.1.65
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  192.168.1.65           12   e8ed.f36a.6310  ARPA   Vlan1
BMT-45959#show mac-ad
BMT-45959#show mac-address-table
Destination Address  Address Type  VLAN  Destination Port
-------------------  ------------  ----  --------------------
b838.61ac.ecfa          Self          1     Vlan1

BMT-45959#

 

And all the outgoing ports on the 887 are configured specifically as access ports.

 

Thanks,

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