BGP Path Selection
Path Selection Problems
| Key Point | Further Details |
|---|---|
| AS_PATH Issues | Look for incorrect AS_PATH configurations that might be influencing path selection improperly. |
| Next-Hop Unreachable | Ensure the next-hop IP address for BGP routes is reachable from the router. |
| Incorrectly Configured Local Preference or MED | Check if these attributes are set correctly as they can influence route selection. |
Palo Alto Commands
| Command | Explanation |
|---|---|
show routing protocol bgp path-info | Displays path information for troubleshooting AS_PATH issues. |
show routing protocol bgp all | Provides a comprehensive overview of all BGP paths and their attributes. |
test routing fib-lookup ip <ip-address> | Verifies if a next-hop IP address is reachable via FIB lookup. |
show routing protocol bgp policy | Displays BGP policies, useful for examining local preference or MED settings. |
Cisco ASA Commands
| Command | Explanation |
|---|---|
show ip bgp | Shows the BGP table with path attributes for route selection analysis. |
show ip bgp neighbors <neighbor> advertised-routes | Checks routes advertised to a specific neighbor, useful for MED and local preference issues. |
ping <next-hop-ip> | Verifies reachability of the next-hop IP address. |
show ip route | Displays the IP routing table to check if next-hop is in the routing table. |
Fortinet Commands
| Command | Explanation |
|---|---|
get router info bgp routes | Displays BGP routes and their attributes for path selection troubleshooting. |
get router info bgp neighbors <neighbor> routes | Shows routes received from a specific neighbor, including path attributes. |
execute ping <next-hop-ip> | Tests the reachability of the next-hop IP address. |
diag ip route list | Lists the IP routing table to verify next-hop reachability. |
Check Point Gaia Commands
| Command | Explanation |
|---|---|
show bgp routes as-path <AS-path> | Filters the BGP table by AS_PATH for troubleshooting. |
show bgp routes detail | Displays detailed BGP route information, including next-hop and path attributes. |
ping <next-hop-ip> | Checks reachability of the next-hop IP address. |
show route all | Verifies if next-hop IP addresses are present in the routing table. |
Debian Commands
| Command | Explanation |
|---|---|
vtysh -c 'show ip bgp' | Displays BGP routes and their path attributes for analysis. |
vtysh -c 'show ip bgp neighbors <neighbor> advertised-routes' | Views routes advertised to a specific neighbor, useful for checking MED and local preferences. |
ping <next-hop-ip> | Tests reachability of the specified next-hop IP address. |
ip route show | Shows the kernel routing table, helpful for verifying next-hop IP reachability. |
Additional Path Selection Considerations
| Key Point | Further Details |
|---|---|
| Weight Attribute Configuration | For vendor-specific devices, check if the weight attribute is correctly applied to influence path selection. |
| BGP Community Tags Usage | Ensure proper usage and interpretation of BGP community tags for route manipulation. |
Palo Alto Commands
| Command | Explanation |
|---|---|
show routing protocol bgp path-info | Displays detailed path information including weight and community tags. |
show routing protocol bgp policy | Displays BGP policies, useful for examining how community tags are applied. |
debug routing bgp update recv | Enables debugging to view incoming BGP updates and their attributes, including community. |
debug routing bgp update send | Enables debugging to view outgoing BGP updates and their attributes, including weight and community. |
Cisco ASA Commands
| Command | Explanation |
|---|---|
show ip bgp | Displays the BGP table, showing paths with their weight and community values. |
show ip bgp community <community> | Filters BGP routes by community tag to analyze their usage and propagation. |
| `show running-config | section route-map` |
show ip bgp neighbors <neighbor> advertised-routes | Shows routes advertised to a specific neighbor, including applied weights and communities. |
Fortinet Commands
| Command | Explanation |
|---|---|
get router info bgp routes | Lists BGP routes, including path attributes like weight and community tags. |
diagnose router bgp routes detail | Provides detailed information on BGP routes, including their community values. |
diagnose router bgp neighbors <neighbor> routes | Displays detailed information about routes received from a neighbor, including community tags. |
get router info bgp summary | Summarizes BGP session information, useful for quick checks on path attributes. |
Check Point Gaia Commands
| Command | Explanation |
|---|---|
show bgp routes community <community> | Filters the BGP table by community tag for troubleshooting. |
show bgp routes detail | Displays detailed information of BGP routes, including their community tags and weight (if applicable). |
show bgp summary | Provides a summary of BGP peers and sessions, useful for overviewing path selection settings. |
show bgp policy | Displays BGP policies, including usage of community tags for route manipulation. |
Debian Commands
| Command | Explanation |
|---|---|
vtysh -c 'show ip bgp' | Shows the BGP table including community tags and possibly weight, if supported. |
vtysh -c 'show ip bgp community <community> | Displays routes with a specific BGP community tag, useful for verifying community usage. |
| `vtysh -c ‘show running-config | include route-map’` |
vtysh -c 'show ip bgp neighbors <neighbor> advertised-routes' | Shows routes advertised to specific neighbors, including any modifications by weight or community. |