To view the contents of all route tables:
tnsr# show route
To view the contents of a single route table:
tnsr# show route table <table name>
For example, to view the default IPv4 route table only, use:
tnsr# show route table ipv4-VRF:0
By default, the output omits entries which may clutter up the list, such as
broadcast routes for each connected subnet, routes which drop traffic, and so
on. To include these entries and view the complete route table, add the
keyword to the end of the command:
tnsr# show route all
tnsr# show route table ipv4-VRF:0 all
To find a route which will be used for a given destination, use:
tnsr# show route table <table name> <prefix> [exact]
This command looks in a route table to find an entry which would be used by TNSR to deliver traffic to the given destination prefix. In other words: It answers the question “How will a packet get from here to there?”.
This command does not filter the route table contents or search for routes with longer prefixes within a given range.
The command supports the following modifiers:
Restricts results to those which exactly match the given prefix.
Route Lookup Example¶
For example, to find the route TNSR will use to deliver traffic for
tnsr# show route table ipv4-VRF:0 10.4.0.1/32 Route Table ipv4-VRF:0 AF: ipv4 ----------------------------------------- 10.4.0.0/24 via 10.2.222.2 ipip1 weight 1 preference 20
In the route display, the
flags: row may contain the following:
- no flags
If the flags line is empty, this is a normal route with no special actions.
This network is local to TNSR and packets to this destination will not leave the TNSR host.
Packets matching this route will be dropped by TNSR. Commonly seen with null routes for subnets or for traffic which must not leave a subnet.
Packets matching this route will be dropped by TNSR, and TNSR will send an ICMP “Destination unreachable” message back to the source address.
Packets matching this route will be dropped by TNSR, and TNSR will send an ICMP “Destination administratively prohibited” message back to the source address.
Routing tables on TNSR may include unexpected entries by default or even after adding and configuring interfaces and other services. The following list covers several of these types of routes that may be present and what they mean:
- 0.0.0.0/32 (drop)
Null route to drop traffic with an empty address.
- 0.0.0.0/0 or ::/0
Default route for packets that do not match any other route, such as for Internet hosts or other remote destinations.
- 188.8.131.52/4 (drop)
Multicast that must not be routed.
Local subnet multicast.
- 240.0.0.0/4 (drop)
Reserved network that must not be routed.
- 255.255.255.255/32 (local)
Special broadcast address for networks local to TNSR.
IPv6 link local.
- x.x.x.<first>/32 (drop)
Null route for subnet configured on an interface. Last octet will vary depending on subnet size and network address. For example, this is
- x.x.x.<last>/32 (drop)
Broadcast address for subnet configured on an interface. Last octet will vary depending on subnet size and network address. For example, this is
- x.x.x.x/32 (via x.x.x.x, local)
Internal route for an IPv4 address present on a TNSR interface.
- x:x:x::x/128 (via x:x:x::x, local)
Internal route for an IPv6 address present on a TNSR interface.
Routes can also be added to the table dynamically by other processes such as via BGP or if an interface is configured as a DHCP client. Check the status or other associated logs for configured features to find the origins of these routes.