BGP Routing Table
The Find BGP Routing Table window, as shown in the following figure, will appear when the Network > Protocols > BGP > BGP Routing Table function is selected. The BGP Routing Table window is used to display all BGP routing from the specified source node to the specified destination node/IP address.
Choose a source node and a destination node (and/or destination IP address) from two different autonomous systems from the drop down lists and then click on the Show Routing Table button. Selecting the SrcAS and DestAS is not required but is only used to filter the Src Node and Dest Node lists. (The Dest AS will be ignored if it is in a different AS than the Destination IP Address entered.) Selecting a blank SrcAS and DestAS field can be done to retrieve back all source and destination nodes from the node drop down lists.
Note that different destination IP addresses may have different attributes and associated routing policies. The destination IP address can be directly entered or populated by first selecting the Dest Node. To load additional IP addresses at that node found in the BGP Subnet window into the drop down list (Network > Protocols > BGP > BGP Subnets...), check “List BGP Subnets.”
If you already know the IP address, you can skip selecting the matching Dest Node or Dest AS, which can be derived from the IP address. Note also that this destination IP address should either be included in one of the BGP subnets (see BGP Subnets for more information), or defined on the destination node.
Another method of choosing the source and destination nodes is to use the mouse and the Standard (not BGP) map. After selecting the Network > Protocols > BGP > BGP Routing Table function, move the mouse over the map. Notice that the arrow of the mouse turns into a cross hair. Click on the first node, which will be the source node. Move the cross hair to another node and click on it to specify the destination node. Then move to the Find BGP Routing Table window and click on the OK button.
Tip: To clearly see which nodes belong to which ASs from the map, go to the Standard map’s Filter menu and make sure that the box for Hide ASNodes/Links is unchecked. You might also use the map’s right-click menu’s Grouping>AutoGroup option and group your nodes by AS and go to the Subviews > AS menu to color the nodes by AS.
Troubleshooting: In some cases the BGP routing table search does not return any results. Make sure that the SrcAS and Dest AS are different. Additionally, check the EBGP neighbor relationships from the BGP map in Network > Maps > Maps (BGP View) to verify whether two routers can communicate using EBGP. Finally, check that the destination IP address is either assigned to the destination node, or a BGP subnet originated from that node.
The BGP Routing Table window shows all possible routes from the specified source node to the specified destination node/IP address. The fields shown on the window are:
Field |
Description |
|---|---|
Src IP Address |
The IP address of the source node. |
Src Node |
The name of the source node. |
Dest IP Address |
The IP address of the destination node. |
Dest Node |
The name of the destination node. |
Exit Src AS |
This shows the router name and IP address for the last BGP speaker on the path before it exits the AS of the source node. |
BGP Next Hop |
The router name and IP address of the BGP next hop. |
Mask |
The corresponding mask of the destination IP address. |
Preference |
This is not a BGP property, but is used to indicate the preferred BGP next hop chosen by the BGP route selection process when there is more than one possible path. Possible values are “Preferred”, “Blocked”, or blank. |
Weight |
The weight attribute |
Local Preference |
The local preference number. |
Med |
The Multi-Exit Discriminator attribute |
AS Path |
The AS path attribute, which consists of AS numbers of all ASs that the route traverses, the most recently traversed one displayed first. |
Community String |
The Community Attribute |
Origin |
The origin attribute indicates how a route was learned (e.g., IGP, EGP, or Incomplete) |
Distance |
Total metric of the IGP route from the router to the Exit Src AS router |
Highlight a BGP route entry and then click on the Show Route button to display the route on the standard map. Or select Show All Routes to display routes for all the BGP Routing Table entries displayed. Note that the gray line symbolizes the connection to the BGP next hop. Click “Show Path” to show the actual path that would be used.