Route Tagging

Route Tagging
Route tagging is used to distinguish routes learned by the different EIGRP sessions. By defining
a different AS number, EIGRP can run multiple sessions on a single router. Routers using the
same AS number speak to each other and share routing information, which includes the routes
learned and the advertisement of topology changes.
Route redistribution, which is covered in its own section later in this chapter, allows routes
learned by one EIGRP AS session to be shared with another session. When route redistribution
occurs, the routes are tagged as being learned from an external EIGRP session. Internal EIGRP
routes have an administrative distance of 90, while external EIGRP routes have a less trusted
administrative distance of 170.