All cisco console ports are not the same that may prevent you from logging in

We are used to cisco console ports to be 9600 N-8-1 with rts/cts control. Some appliances don't support RTS, so if you set the boot up sequence but cannot get to login, playing with flow control may do the trick. If your terminal server or software gives you the status of the leads like WTI, do the port diag to see if RTS is up

DHCP reservations that depend on MAC addresses may fail if the server uses option 61 with UUID

DHCP issue has to do with the Intel NIC and what looks like the newest firmware changing how DHCP leases are requested. Basically, with the newest firmware (it appears) the Intel NIC is using UUID over option 61 to request a DHCP address. Unfortunately, our reservations have always been based on MAC address in the past. So, probably the easiest thing is to have HP investigate intel firmware for a version that uses MAC for Option 61 or request a change to the firmware to use MAC for option 61.

Mainframe OSAs and trigger BPDU guard and error disables switch port

When you upgrade microcode on IBM OSAs when they come back up they may act as a 'bridge' and send BPDUs to your switch which fires bpudguard. You do not want to change the switch. what you have done is have the mainframe people stop and start the OSA, make sure the UCB is not 'boxed', and you should be fine.

NX-OS changes how type 5 external routes work

NX-OS supports and rfc 2328 which says that if there are two paths to an ASBR one through area 0 and one that is not the NON AREA 0 is what is preferred. So when you move to nexus devices or add new routers, two type 5 external routes may not be put in as equal cost routes even though all the costs are equal. So you may need to add a non 0 area to your new router to get the load balancing you want. There are other factors to be considered in complex topologies see http://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/117824-config-ospf-00.html

You do not get a default route in a stub area without an ABR (link in A 0)

I use Vrf Lite a lot and there you use stub areas, sometimes I have a local segment (The VRF is on a single distribution pair) and then need to expand it, or I am building a VRF that statically routes to a firewall. To get a default route, that has to come from an ABR, so some interface has to be in Area 0. If you are statically routing to a firewall make the interfaces routing to that firewall area 0 interfaces and then the switch that has the firewall connection sends out a default route to any other routers in the VRF

Port channels on different line card types and qos

If you enable qos you perform buffer carving (allocation of buffers) and the creation of queues. Many card based hardware platforms like the 6500 have different queueing and buffer architectures between different card types. What this means is that if you enable QoS ports that were in a port channel get suspended because the QoS parms do not match. If you do not run LACP you can end up with a great deal of trouble.

removing a BGP router

When you wnat to remove a device that is running IBGP, you have to watch where IBGP sessions can form. I was removing a router with had IBGP configured on it to another router at a site that was connected to MPLS providers. The LAN interfaces were shut down. What happened next was since the router loopbacks (the IBGP neighbors) were put into the provider and IBGP session would form through the providers with a long as path. Now you would think that BGP split horizon would prevent router A from learning about router B, BUT if you have a default route, traffic will flow to your data center that will know about both loopbacks via the providers and will route traffic between them Then prefixes for the local subnets began to flow to the router that had no connection to the local networks. Then that router advertised them to the provider so traffic started to flow to a router that could not forward any of that traffic. Finally router A would send via IBGP its own loopback that would point to a local route, since router B was not connected to the any LANs once that IBGP advertisement of the loopback arrived, the IBGP session would time out, then the local based loopback prefix gets removed the prefix advertised by the provider comes back. THUS the ibgp peer goes up and down in a 90 second sequence. Net of this is that if you are removing a device from the network, first thing to do is to shut down dynamic routing to that box, add any static routes to say loopbacks you need and a default route to the device being removed, then after a while shut down the interfaces.