interconnecting two core switches

[XEmmeX]

Hi all,

I need to connect two Cisco C4500X, using a 1000BaseLH transceiver.

Each core switch manage its own VLANs. I just need to connect the two core switches and use this link for routing purpose.

I created a transport vlan on two devices, with same Vlan tag number. 

On CS1 I set up 10.0.0.1 as Transport Vlan ip address.

On CS2 I set up 10.0.0.2 as Transport Vlan ip address.

On CS1 transceiver port I set up:

switchport mode trunk

switchport trunk allowed vlan *transporttag*

The same I did on CS2 transceiver port.

It seems it doesn't work 'cause I can ping CS2 from CS1 and viceversa.

Any ideas?

[Jon Marshall]

Okay, that makes sense.

From each VSS pair please post "sh int vlan 117".

Jon

[XEmmeX]

Vlan117 is up, line protocol is up
Hardware is Ethernet SVI, address is 0008.e3ff.fd90 (bia 0008.e3ff.fd90)
Description: ***Link TA-TA2***
Internet address is 10.0.0.2/29
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive not supported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 4d14h, output never, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
L3 in Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes
L3 out Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes
IPv6 L3 in Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes
IPv6 L3 out Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
97 packets output, 4462 bytes, 0 underruns
0 output errors, 1 interface resets
0 unknown protocol drops
0 output buffer failures, 0 output buffers swapped out

Vlan117 is up, line protocol is up
Hardware is Ethernet SVI, address is 0008.e3ff.fd90 (bia 0008.e3ff.fd90)
Description: ***Link TA-TA2***
Internet address is 10.0.0.1/29
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive not supported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:53:16, output never, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
L3 in Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes
L3 out Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes
IPv6 L3 in Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes
IPv6 L3 out Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
120 packets output, 7116 bytes, 0 underruns
0 output errors, 1 interface resets
0 unknown protocol drops
0 output buffer failures, 0 output buffers swapped out

[Jon Marshall · Accepted solution]

If you look at the mac addresses of both interfaces they are the same and this is because you are using the same domain ID.

Which means the pings will never work because the same mac address is local to each switch.

See this for more details  -

http://0wned.it/2015/02/07/vss-and-virtual-mac-address-pool/

Jon

[XEmmeX]

Thank you so much Jon

now it's pretty clear. 

According to your article, the fastest way is to assign a static mac-address to physical interface. Problem is that "mac-address" command is not present :-/

[Jon Marshall]

Never had to do it before so not sure what is and isn't available.

Changing the domain ID would be the best solution but obviously that needs downtime.

Perhaps try "no switchport" under the physical interfaces and see if you can assign a mac address to the interface ?

Jon

[XEmmeX]

nope but nevermind. Probably I'll change VSS domain number :-/

That's the only solution, unless you won't add a router between the two CS and let it manage the routing

[Jon Marshall]

I don't think adding a router would help to be honest because it would be seeing the same mac address for two different IPs in it's arp table.

Like you say I think the best thing is to change the domain ID of one of the VSS pairs.

Jon

[XEmmeX]

Hi Jon,

just one more question. Is it safely to change VSS domain number?

As far as I know, I can do it by these commands:

switch virtual domain 20
switch convert mode virtual

Is it right? VSS are in production, so I just need to know if there could be any problem (by the way VSS will be reloaded after configurated)

[Jon Marshall]

Can you post a "sh int vlan 117" from both switches ?

Jon