Discrepancy between interface labels on GNS3 client and NX-OS appliance physical connection

Recently, I had to spin up NX-OS topology for the project I’m working on but I’ve been failing miserable. Nothing wants to work, simple L2 like CDP, L3 including VRF and IGP, FHRP etc..

Basically, everything is broken where physical links seems to be connected (protocol/state).  This makes me question myself if I even know what I’m doing.

Environment is running on the newest GNS3 Client (2.1.6 as of postdate) with titanium-final.7.3.0.D1.1.qcow2 for NX-OS.

After long troubleshooting session I’ve found out that interface labels on GNS3 are actually NOT how physical uplinks are connected. Configuring your scripts on wrong interfaces WILL make your life miserable – trust me. Let me give you an example.

By default, all interfaces on N7K modules are down so you have to enable them:

sw1(config-if)# int e2/1-48 ; no shut ; int e3/1-48 ; no shut ; int e4/1-48 ; no shut

Note, even though VDC shows three modules GNS3 will only allow you to connect to module 2  on port 1-14.

sw1# sh run vdc

!Command: show running-config vdc
!Time: Thu May 24 19:07:45 2018

version 7.3(0)D1(1)
vdc sw1 id 1
limit-resource module-type m1 m1xl m2xl f2e
allocate interface Ethernet2/1-48
allocate interface Ethernet3/1-48
allocate interface Ethernet4/1-48
limit-resource vlan minimum 16 maximum 4094
limit-resource vrf minimum 2 maximum 4096
limit-resource port-channel minimum 0 maximum 768
limit-resource u4route-mem minimum 96 maximum 96
limit-resource u6route-mem minimum 24 maximum 24
limit-resource m4route-mem minimum 58 maximum 58
limit-resource m6route-mem minimum 8 maximum 8

Back to the discrepancy. Look at the Fig.1 and Fig.2 showing first set of N7Ks (sw1 and sw2) uplink.  Fig.1 shows interface label (from GNS3) as physical interfaces to be on e2/14 on both switches, but what CDP really shows is different (Fig.2).

sw1_sw2_GNS3_visual_label
Fig.1 – GNS3 Interface label showing physical connection to be on e2/14
sw1_cdp_ne
Fig.2 – CDP pull from SW1 showing physical relationship with SW2

As you can see L1 from module standpoint is on e2/15 on both sides. If you are trying to configure L3 between these two on e2/14s and uplinks are not coming up now you know why.

This makes me think if we have one up logic issue here but no.  I.e. connection on e2/2 on both switches (Fig.2) matches on both label side on GNS3 as well as physical. So, there is definitely some kind of a glitch that will make you nuts if you trying to configure topology based on the labels from GNS3.

Same scenario between sw3 and sw2 uplink (Fig.3 and Fig.4) where you can see the mismatch.

sw3_sw2_GNS3_visual_label
Fig.3 – GNS3 Interface label showing physical connection to be on e2/3
sw3_cdp_ne
Fig.4 – CDP pull from SW3 showing physical relationship with SW2

If anybody experienced the same issue AND was able to remediate it, please drop a comment. Otherwise, be aware of the issue and configure your devices based on CDP output rather than GNS3 interface labels.

Regards,
Bart

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