Traffic Flow in the vPC Environment

[Ibrahim Jamil]

Hello Overseas Freinds

Greeting

Pls Find Below Topology

The Question is that

what would happend to HTTP Traffic going from server 1 to Server 2 if the G0/0 on n7k-switch-1 Failed and the G0/1 Failed on n7k-Switch-2  ?

the peer-link did it pass Traffic ?

pls not These 2 Commands peer-switch and peer-gateway have been configured on the vpc domain 100 between SW1 and SW2 and what if its not configured

Thanks

Ibrahim Jamil

ME - Dead Sea

 

 

[f00z]

If it's properly set up, then switch1 and switch2 have SVI with HSRP or whatever, if it's routing. If it's layer2 and switches have no routing then it's much simpler.   

If layer2, traffic gets hashed to switch 1, then switch 1 sends it out the only link available, which is the peer link to switch2, and then switch2 sends it to the server1.

If it's routing, switch1 will layer3 lookup the packet, then find the adjacency which is a mac addr on vlan10, and forward like the layer2 above.

When normal conditons, switch1 and switch2 both see the mac addr for server1 on the VPC that connects to the server, if the port on switch1 dies, then switch1 sees the mac address of server1 on the peer link.  It will never be on the peer link unless ALL VPC members on that switch are down (that connect to the server, it could have more than 1 link for example) and it has no other way to get to it.

[Ibrahim Jamil]

Hello bro

Can u elaborate more for traffic perspective? 

pls not These 2 Commands peer-switch and peer-gateway have been configured on the vpc domain 100 between SW1 and SW2 and what if its not configured

[f00z]

I think I answered it pretty well. I mean the whole purpose of the peer-link is so it has a backup way to send traffic if one of the vPC members fails. So in your diagram there the server2 only has one way to send layer2 traffic, which is to switch 1, and server 2 only has 1 way also, which is switch2 , so it would go server 1 -> switch 1 ->(peerlink) switch 2 -> server2.

In this case the peer-switch and peer-gateway would have 0 effect on anything as both servers are in vPC and there is no layer3 routing on the switches , both servers are in vlan10 i assume from the diagram, and there is no ip routing is configured on switch1 or 2

[Ibrahim Jamil]

Hi Boss

Thanks for ur Answer

mmm , lets change the Scenario a bit if u pls

what if server 1 in VLAN 10 whereas server 2 in VLAN 20 , now how the Traffic flow behave

thanks

[f00z · Accepted solution]

Traffic flow will be the same, just a little different lookups internally.

What's the layer3 config? HSRP active/active on vlan 10 and 20 ? 

That's the normal way to set up layer3 VPC; So server1 would send to HSRP VMAC of vlan 10 svi which switch 1 would receive and switch 1 will do layer3 lookup for destination of server2, which is on vlan 20 svi, and send it to the adjacency (server2 mac) on vlan 20 and since the server2 mac addr is only available over peer link, it continues like I said above.  

[Ibrahim Jamil]

thank y my freind