IS-IS Extensions to Support Route Tagging
To control the transmission of routes into IS-IS, or to control transmission of IS-IS routes between different IS-IS levels, you can tag routes with certain attributes. IS-IS routes can carry these attributes, which the routing policies can use to export and import routes between different IS-IS levels. A sub-TLV to the IP prefix TLV is used to carry the tag or attribute on the routes.
Route tagging does not work when IS-IS traffic engineering is disabled.
protocols {
isis {
export tag-lo0;
}
}
policy-options {
policy-statement tag-lo0 {
from {
interface lo0.0;
}
then {
accept;
tag 200;
}
}
}
You can verify that the tag has been correctly applied by using
the show isis database extensive command. In the command
output, look for the Administrative tag field.
After verifying that the routes are tagged correctly, you can apply a route leaking policy to match against the presence of administrative tags, rather than specifying a list of route filters.
protocols {
isis {
export leak-tagged-L2-to-L1;
}
}
policy-options {
policy-statement leak-tagged-L2-to-L1 {
from {
tag 200;
protocol isis;
level 2;
}
to {
protocol isis;
level 1;
}
then accept;
}
}