Tips of BGP Convergence

1. tweak BGP timers (Hello, Advert, Scan)

2. rely on IGP (fine tune IGP first)

bgp fast-external-fallover (default enable for eBGP)

bgp nexthop trigger delay delay-timer (seconds)

3. enable BFD
neighbor 1.1.1.1 fall-over bfd

4. allow multiple paths in BGP
a) using different RD (MP-BGP)
b) different RRs has different perference for a prefix
c) BGP The “Add Paths” capability

Very good reference:Understanding BGP Convergence
BGP Commands: 
BGP Support for Next-Hop Address Tracking

Bidirectional Forwarding Detection

BFD is a detection protocol designed to provide fast forwarding path failure detection times for all media types, encapsulations, topologies, and routing protocols. In addition to fast forwarding path failure detection, BFD provides a consistent failure detection method for network administrators. Because the network administrator can use BFD to detect forwarding path failures at a uniform rate, rather than the variable rates for different routing protocol hello mechanisms, network profiling and planning will be easier, and reconvergence time will be consistent and predictable. 

A maximum 100 sessions per line card are supported for the distributed Cisco 12000 series Internet router. The minimum hello interval is 50 ms with up to three Max retries for a BFD control packet to be received from a remote system before a session with a neighbor is declared down. 

Configuring BFD Support for BGP 

SUMMARY STEPS

interface FastEthernet 0/1

 ip address 1.1.1.1 255.255.255.0

 bfd interval 50 min_rx 50 multiplier 3

1. enable

2. configure terminal

3. router bgp as-tag

4. neighbor ip-address fall-over bfd

5. end

6. show bfd neighbors [details]

7. show ip bgp neighbor 

Configuring BFD Support for IS-IS for One or More Interfaces 

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type number

4. isis bfd [disable]

5. end

6. show bfd neighbors [details]

7. show clns interface 

Ref:

http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/fs_bfd.html#wp1153100 

http://www.cisco.com/en/US/docs/ios-xml/ios/iproute_bfd/configuration/12-2sr/Bidirectional_Forwarding_Detection.html#GUID-5EF281D7-048D-42C6-81F8-D50524CE24AD