Nexus 5548 fex interface configuration in vPC scenario

[fuhrersk8]

Hello Forum Team!

I have a pair of Nexus 5548UP configured as a vPC domain active-standby couple with six Nexus 2248TP Fex's in a dual-homed scenario (each fex is connected to each 5548UP). At the same time, both 5548UP are dual-homed to a pair of VSS Catalyst 6509.

I have a couple of questions regarding performance and configuration:

1. When configuring a fex interface, I've noticed that if the configuration is not the same or replicated on both 5548UP, the fex interface won't come up; is this normal behaviour? For now I am replicating manually the configuration on both 5548UP (not confyg-sync).

2. When performing ICMP tests from the 2248TP to the VSS, the response time is around 1ms to 2ms; from the 5548UP to the VSS pair is approximately 0.5ms. Is that normal delay response time from the 2248TP? I was expecting less response time from the 2248TP (the fex's have 20 Gigs of uplink bandwidth to the 5548UP pair and the 5548UP pair have 40 gig's of bandwidth to the VSS pair).

Thanks in advanced team!

[Reza Sharifi · Accepted solution]

Hi,

1. When configuring a fex interface, I've noticed that if the configuration is not the same or replicated on both 5548UP, the fex interface won't come up; is this normal behaviour?

Yes, that is a normal behavior.  Since yours FEXes are connected to BOTH 5ks, you have to configure both 5Ks in order for the FEX to come up. If you connect your FEX physically to only one 5k, then you only configurethat one 5k, but in your case you need to configure both 5ks exactly the same.

2. When performing ICMP tests from the 2248TP to the VSS, the response time is around 1ms to 2ms; from the 5548UP to the VSS pair is approximately 0.5ms. Is that normal delay response time from the 2248TP? I was expecting less response time from the 2248TP (the fex's have 20 Gigs of uplink bandwidth to the 5548UP pair and the 5548UP pair have 40 gig's of bandwidth to the VSS pair).

I have never tested this, but I would think since the 2k needs to to 5k for every packet including talking to another host on the same 2k, the delay would slightly be higher then when you ping directly from the 5k.

HTH

[fuhrersk8]

  One clarification, I am reffering to FEXes host interfaces, for example interface Ethernet101/1/1. Still this apply?

Thanks again for your support!

[Reza Sharifi · Accepted solution]

Hi,

That is correct.  Every time you configure an end device connecting to a FEX, you need to do the same exact config on both 5ks, if not it will not work.

example

inter 101/1/1

switchport mode access

switchport access vlan 20

above config needs to be applied to both 5ks for the same interface.

HTH

[fuhrersk8]

Excellent. Thanks again for your great support!

[Reza Sharifi]

Glad to help

Good Luck and thanks for the rating.

[fuhrersk8]

  Excellent and thanks for your reply Reza!

  Regards,