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ohforce55
Beginner

Help! Mac address shows ports as Router..

Hi,

I knew this but totally got about this for a moment.

I will very appreciate if you can remind me.

If I look at the mac address table, the ports says 'Router' (BOLD).

What does that mean?

xx-2#sh ip arp 10.18.30.35
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.18.30.35 - 5c50.156a.8c00 ARPA Vlan848
enc-wups-sn-r6509-2#
enc-wups-sn-r6509-2#
xx-2#sh mac add add 5c50.156a.8c00

Legend: * - primary entry
age - seconds since last seen
n/a - not available
S - secure entry
R - router's gateway mac address entry
D - Duplicate mac address entry

Displaying entries from DFC linecard [2]:

vlan mac address type learn age ports
----+----+---------------+-------+-----+----------+-----------------------------
R 399 5c50.156a.8c00 static No - Router
R 300 5c50.156a.8c00 static No - Router

12 REPLIES 12
Iulian Vaideanu
Enthusiast

That's probably the router's own IP address on that interface... what does "sh run int vlan848" look like?

Hi,

Thank you for your reply!

This is a L3 Switch. Then why doesn't it show what port that vlan belongs to unlike the others?

Also, when I type sh ip arp <other IP address>, nothings comes out. What does that mean when I don't get any output?

Thanks!

If the MAC address is that of a SVI of the router itself, how can it belong to a physical port?

If "sh ip arp <IP>" doesn't show anything it means that the router can't associate that IP to a MAC address (maybe the device configured with that IP address is powered off or disconnected for example).

Hi,

Thanks for your reply again. 

I see that the interface is up up but still doesn't show the output..

GRANT3779
Frequent Contributor

What is the output of the following on the switch

show ip interface brief

Getting a bit lost as to what your are looking for now :-)

What I mean is that 

Let's assume vlan 400 is data vlan. And a user is using it thru switch.

If I do sh ip arp <a users's IP> and the sh mac ad ad <user's mac>, I'm supposed to see the physical port. For instance Gi1/12 something like this..

But why does this show the port as 'Router'?

Vlan400                10.18.17.131    YES NVRAM  up                    up 

enc-wups-sn-r6509-2#sh ip arp 10.18.17.131
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.18.17.131 - 5c50.156a.8c00 ARPA Vlan400
enc-wups-sn-r6509-2#sh mac ad ad 5c50.156a.8c00

Legend: * - primary entry
age - seconds since last seen
n/a - not available
S - secure entry
R - router's gateway mac address entry
D - Duplicate mac address entry

Displaying entries from DFC linecard [2]:

vlan mac address type learn age ports
----+----+---------------+-------+-----+----------+-----------------------------
R 399 5c50.156a.8c00 static No - Router
R 300 5c50.156a.8c00 static No - Router

GRANT3779
Frequent Contributor

I see now.

What is the output of

show ip int brief

from your switch

enc-wups-sn-r6509-2#sh ip int b
Interface IP-Address OK? Method Status Protocol

Vlan400                10.18.17.131    YES NVRAM  up                    up 

GRANT3779
Frequent Contributor

Do you have a vlan interface 848?

sh run int vlan 848?

what are all the addresses from 

show ip int brief

GRANT3779
Frequent Contributor

Is this a Layer 3 switch?

As an example - I have the following SVI, amongst others on a 6880X - 10.44.0.1

Vlan500 10.44.0.1 YES NVRAM up up

UK-CORE-01#sh arp 10.44.0.1
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.44.0.1 - 00c1.64a0.1300 ARPA Vlan500



UK-CORE-01#sh mac address-table | inc 00c1.64a0.1300
R 645 00c1.64a0.1300 static No - Router
R 641 00c1.64a0.1300 static No - Router
R 519 00c1.64a0.1300 static No - Router
R 523 00c1.64a0.1300 static No - Router
R 868 00c1.64a0.1300 static No - Router

It is referencing a local address tied to the logical interfaces.

Hi,

Thank you four your reply!

Yes it is L3 switch (6800).

Grant, I'm sorry bur I don't quite understand the last statement.

'It is referencing a local address tied to the logical interfaces.'...

Would you please explain in more detail?

GRANT3779
Frequent Contributor

See output below  -
I have multiple virtual L3 interfaces configured on my Layer 3 switch. I have only shown some of them below but it is the same for them all. The MAC is tied to the layer 3 interfaces you have created.
UK-CORE-01#show ip int brief
Interface              IP-Address      OK? Method Status                Protocol
Vlan99                 10.44.99.2      YES manual up                    up
Vlan501                10.44.1.1       YES manual up                    up
Vlan502                10.44.2.1       YES manual up                    up
Vlan503                10.44.3.1       YES manual up                    up
Vlan519                10.44.19.1      YES manual up                    up

UK-CORE-01#sh int vlan 99
Vlan99 is up, line protocol is up
  Hardware is EtherSVI, address is 00c1.64a0.1300 (bia 00c1.64a0.1300)
UK-CORE-01#sh int vlan 501
Vlan501 is up, line protocol is up
  Hardware is EtherSVI, address is 00c1.64a0.1300 (bia 00c1.64a0.1300)

UK-CORE-01#sh int vlan 503
Vlan503 is up, line protocol is up
  Hardware is EtherSVI, address is 00c1.64a0.1300 (bia 00c1.64a0.1300)

UK-CORE-01#                sh mac address-table | inc 1300
  R    99 00c1.64a0.1300   static   No       -      Router
  R   503 00c1.64a0.1300   static   No       -      Router

  R   501 00c1.64a0.1300   static   No       -      Router