Hello all.
This is my first post and i'll try to be as detailed as possible. I am upgrading the core of our network with two NX 6004's that are connecting north to two Catalyst 7606's. The 6004's also have connections going south to two NX 6001's. Everything is eBGP with all P2P links, detailed like this: (for clarity sake, i'm just going to use a single of each box)
7606 -> 6004 (Port-Channel - two 10Gb links on both sides)
6004 -> 6001 (40Gb P2P)
The eBGP peerings between the NX boxes come up just fine. The peerings between the 6004 and the 7606 does not come up what so ever. After digging around and debugging some bgp packets, I noticed that TCP never establishes what so ever. Forgetting about BGP for the moment, I then noticed when I run some pings from the 7606 with the df-bit set and a size of 1500 and a count of 100 (per se), every 15th packet is dropped, consistently. If I were to change the size up or down, it affects the dropped packet but at different intervals. For example, send a packet size of 1100, and its every 25th packet. Send a size of 8000 (when trying to set MTU manually on the interface), every 3rd packet was dropped. Here is what I have done so far:
Set MTU manually
Set P2P to a single link only
WireShark the link (no good info aside from no tcp response, which didn't yield much)
Wipe the NX box clean and only configured interface
IP TCP PATH-MTU-DISCOVERY was enabled globally on the 7606. I added it to the 6004
Configured static speed and duplex settings
I'm certain I've done a lot more that I cannot think of at the moment (have it documented at work). When I run the debug ip tcp transactions, I notice that the syn_sent to the neighbor (when originally trying to setup bgp) was timing out. It almost appears as though this is some buffer or window issue with the NX box but I am coming up short in my research of how to potentially fix this. Before I call TAC, I figured i'd post this.
I'm 99% certain its not a fiber issue or L1 issue as both NX boxes which have redundant P2P links to both 7606's are having this same exact issue. I'm also leaning on the fact of a potential bug between IOS and NX-OS; not too sure.
Any help would be appreciated.
Thanks.
-Michael
