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Highlighted
Contributor

AD ,static route next hop or exit int

Hi everybody

Please consider the static routes below:

R1#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route

Gateway of last resort is 200.200.200.3 to network 0.0.0.0

C 200.200.200.0/24 is directly connected, FastEthernet0/0
C 199.199.199.0/24 is directly connected, Vlan1
S* 0.0.0.0/0 [1/0] via 200.200.200.3
is directly connected, FastEthernet0/0

R1#show version

Cisco IOS Software, 2600 Software (C2691-ADVIPSERVICESK9-M), Version 12.4(15)T6, RELEASE SOFTWARE (fc2)

Technical Support:

=================================================================================================


According to following link( I quoted below), in ios version 12.2 or later, static route configured with next hop has AD of 1 while static route configured with exit int has AD of 1°. AD of 1° is preferred to 1 . AD 1° lies between 0 to 1.

Since R1 has ios 12.4 therefore R1 should prefer static route configured using exit int over static route configured using next hop. But if you look at the routing table above, R1 has installed both routes i.e static route configured with next hop and static route configured with exit int.

Based on the following link, R1 should have installed static route configured with exit int only because its Ad of 1° is better than AD of 1 of static route configured with next hop.

I will appreciate your input.

thanks.

http://en.wikipedia.org/wiki/Administrative_distance

The following table gives the default administrative distances used by Cisco routers.

ProtocolAdministrative distance
Directly connected route0
Static route out an interface
Static route to next-hop address1
EIGRP summary route5
External BGP20
Internal EIGRP90
IGRP100
OSPF110
IS-IS115
RIP120
EGP140
ODR160
External EIGRP170
Internal BGP200
DHCP-learned254
Unknown255

Notes:

  • An administrative distance of 255 will cause the router to disbelieve the route entirely and not use it.
  • Since IOS 12.2, the administrative distance of a static route with an exit interface is 1. Prior to the release of 12.2 it was in fact 0.

° Actual administrative distance is recognized somewhere between 0 and 1. This AD is more trustworthy than 1 but less trustworthy than 0.

2 ACCEPTED SOLUTIONS

Accepted Solutions
Highlighted
Advisor

Hi,

this table is incorrect. All static routes have an AD of 1 and there is no such thing as decimal AD.

So what you observe is normal behaviour.

Regards.

Alain

Don't forget to rate helpful posts.

Don't forget to rate helpful posts.

View solution in original post

Highlighted
Participant

Hi Sarah,

Administrative distance is the feature that routers use in order to select the best path when there are two or more different routes to the same destination from two different routing protocols

Here is the table from cisco

Route Source

Default Distance Values

Connected interface

0

Static route

1

Enhanced Interior Gateway Routing Protocol (EIGRP) summary route

5

External Border Gateway Protocol (BGP)

20

Internal EIGRP

90

IGRP

100

OSPF

110

Intermediate System-to-Intermediate System (IS-IS)

115

Routing Information Protocol (RIP)

120

Exterior Gateway Protocol (EGP)

140

On Demand Routing (ODR)

160

External EIGRP

170

Internal BGP

200

Unknown*

255

* If the administrative distance is 255, the router does not believe the source of that route and does not install the route in the routing table.

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094195.shtml

hope this will help.

thanks

View solution in original post

2 REPLIES 2
Highlighted
Advisor

Hi,

this table is incorrect. All static routes have an AD of 1 and there is no such thing as decimal AD.

So what you observe is normal behaviour.

Regards.

Alain

Don't forget to rate helpful posts.

Don't forget to rate helpful posts.

View solution in original post

Highlighted
Participant

Hi Sarah,

Administrative distance is the feature that routers use in order to select the best path when there are two or more different routes to the same destination from two different routing protocols

Here is the table from cisco

Route Source

Default Distance Values

Connected interface

0

Static route

1

Enhanced Interior Gateway Routing Protocol (EIGRP) summary route

5

External Border Gateway Protocol (BGP)

20

Internal EIGRP

90

IGRP

100

OSPF

110

Intermediate System-to-Intermediate System (IS-IS)

115

Routing Information Protocol (RIP)

120

Exterior Gateway Protocol (EGP)

140

On Demand Routing (ODR)

160

External EIGRP

170

Internal BGP

200

Unknown*

255

* If the administrative distance is 255, the router does not believe the source of that route and does not install the route in the routing table.

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094195.shtml

hope this will help.

thanks

View solution in original post

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