Main Troubleshooting Flowchart

Troubleshooting BGP Neighbor Establishment

Note: *Sample log messages to be checked when neighbor is not coming up:

BGP_SESSION-5-ADJCHANGE: neighbor[ip address] IPv4 Unicast topology base removed
  from session Peer closed the session
BGP_SESSION-5-ADJCHANGE: neighbor[ip address] IPv4 Unicast topology base removed
  from session Unknown path error

Note: **Example of ping with packet size and enable does not fragment bit in IP header:

Router#ping 10.10.10.2 size 1400 df-bit

Type escape sequence to abort.
Sending 5, 1400-byte ICMP Echos to 10.10.10.2, timeout is 2 seconds:
Packet sent with the DF bit set
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/37/84 ms

Troubleshooting Routes Missing from the Routing Table

Note: In the debug ip bgp x.x.x.x updates command, x.x.x.x is the neighbor to which the route should be advertised.

Troubleshooting Multihoming Inbound

Troubleshooting BGP Route Advertisement

Troubleshooting Multihoming Outbound

Source:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008009478a.shtml#bgp_trouble_neighbor

show ip bgp neighbors <x.x.x.x> advertised-routes
This shows you the routes that you advertised to this peer.

show ip bgp neighbors <x.x.x.x> routes
This shows you the routes you received from this peer that made it through the inbound filters.

show ip bgp neighbors <x.x.x.x> received-routes
This shows you the routes you received from this peer, even those that were denied(filtered).

In order to use this last command you must configure:
 bgp <as>
 neighbor <x.x.x.x> soft-reconfiguration inbound

User Defined Source Port Ranges for PAT Overview

In order for VoIP traffic to not be in violation of the RTP standards and best practices, even/odd pairing of ports for RTP and RTCP traffic for SIP ALG, Skinny and H.323 has been made available.

Following is a scenario of what happens to VoIP traffic translated using PAT without user defined ports.

The first VoIP traffic getting translated using PAT, would request for port 16384 and would get to use port 16384 for its RTP traffic.

The second VoIP traffic stream getting translated using PAT would also request 16384 for its RTP. Since this port number is already in use by the first call, PAT would translate the 16384 source port for the second phone to 1024 (assuming the port was free) and this would be in violation of the RTP standards/best practices.

A third call would end up using port 1025 and others would increment from there.

Each call after the first call would end up having its inside source port translated to an external port assignment that is out of specifications for RTP, and this would continue until PAT binding fir the first call expires.

Problems associated with RTP traffic being assigned to a non-standard port by PAT:

•Inability for compressed RTP (cRTP) to be invoked in the return direction, as it only operates on RTP flows with compliant port numbers.

•Difficulty in properly classifying voice traffic for corresponding QoS treatment.

•Violation of standard firewall policies that specifically account for RTP/TRCP traffic by specified standard port range.

Here is an example from a debug ip nat sip I did:
02:02:14: NAT: SIP: [1] translate embedded port 1029->5060

Here is an example from show ip nat trans:
Pro Inside global      Inside local       Outside local      Outside global
udp 192.1.271:1024 10.1.1.252:5060   192.168.8.13:5060 192.168.8.13:5060

Even Port Parity

Cisco IOS NAT SIP gateways normally select the next available port+1 for SIP fixup in the NAT translations. The NAT gateway does not check for even/odd pair for RTP/TRCP port numbers, and as a result issues may arise with SIP user agents that are strictly following the encouraged even/odd parity for RTP/RTCP port numbers.

Even port parity for SIP, H.323, and skinny is supported by default and it can be turned off forcing the odd RTP ports allocation.

User Defined Source Port Ranges for PAT: Example

The following examples shows how to assign a set of ports and associate a map to them.

ip nat portmap NAT-I

 cisco-rtp-h323-low
 appl sip-rtp startport 32128 size 128
 appl sip-rtp startport 32000 size 64
ip nat inside source list 1 pool A overload portmap NAT-I

Table 1 Macro Names and Ports

Configuration Examples for Even Port Parity

Even Port Parity: Example

The following example enables even port parity for H.323.

ip nat service allow-h323-even-rtp-ports

The following example enables even port parity for SIP.

ip nat service allow-sip-even-rtp-ports

The following example enables even port parity for the skinny protocol.

ip nat service allow-skinny-even-rtp-ports

source: http://www.cisco.com/en/US/docs/ios/ipaddr/configuration/guide/iad_pat_pt_rng.html

http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6586/ps6640/prod_white_paper0900aecd80597bc7.html

BGP neighbor failover taking too long.

Try lowering the timer values. BGP will use the lower value.
Try using neighbor ip-address fall-over [bfd | route-map map-name]
Try using OER/PfR

ICMP Echo Example
The following example, starting in global configuration mode, configures an active probe using an ICMP echo (ping) message. The 10.5.5.55 address is the target. No explicit configuration is required on the target device.

Router(config)# oer master
Router(config-oer-mc)# active-probe echo 10.5.5.55

TCP Connection Example
The following example, starting in global configuration mode, configures an active probe using a TCP connection message. The 10.5.55.56 address is the target. The target port number must be specified when configuring this type of probe.

Router(config)# oer master
Router(config-oer-mc)# active-probe tcp-conn 10.5.5.56 target-port 23