route-tag (OSPF view)

Use route-tag to configure an external route tag for redistributed VPN routes.

Use undo route-tag to restore the default.

Syntax

route-tag tag-value

undo route-tag

Default

If BGP runs within an MPLS backbone, and the BGP AS number is not greater than 65535, the first two octets of the external route tag are 0xD000, and the last two octets are the local BGP AS number. For example, if the local BGP AS number is 100, the external route tag value is 3489661028 (100 + the decimal value of 0xD0000000). If the AS number is greater than 65535, the external route tag is 0.

Views

OSPF view

Predefined user roles

network-admin

Parameters

tag-value: Specifies the external route tag for redistributed VPN routes, in the range of 0 to 4294967295.

Usage guidelines

In a dual-homed scenario where OSPF runs between the CE and the connected PEs (PE-A and PE-B, for example), you can use external route tags to avoid routing loops.

PE-A redistributes BGP routes from the peer PE into OSPF, and advertises these routes in the Type 5 or 7 LSAs to the CE. In these LSAs, PE-A adds the locally configured external route tag.

When PE-B receives the Type 5 or 7 LSAs advertised by the CE, it compares the external route tag in the LSAs with the locally configured tag. If they are the same, PE-B ignores the LSA in route calculation to avoid routing loops.

The commands used to configure the external route tag (in the descending order of tag priority) are as follows:

• import-route

• route-tag (for PEs) and default tag (for CEs and MCEs)

As a best practice, configure the same external route tag for PEs in the same area.

An external route tag is not transferred in any BGP extended community attribute. It takes effect only on the PEs that receive BGP routes and generate OSPF Type 5 or 7 LSAs.

You can configure the same external route tag for different OSPF processes.

Examples

# In OSPF process 100, set the external route tag to 100 for redistributed VPN routes.

<Sysname> system-view
[Sysname] ospf 100
[Sysname-ospf-100] route-tag 100

Related commands

default (Layer 3—IP Routing Command Reference)

import-route (Layer 3—IP Routing Command Reference)