Help Understanding Offset-Lists Better
Danielh22185
Member Posts: 1,195 ■■■■□□□□□□
in CCNP
I am playing around with off-set lists trying to understand how they operate a bit better. In my topology I am performing multi-point redistribution between ospf and eigrp. I am attempting to influence a route learned from OSPF to take a different path via an off-set list. What I found interesting is when I enter the command:
offset-list 1 in 100000 -- this command increments the metric of the network I am targeting with access-list 1. However it does NOT seem to influence the path.
Then when I enter the command:
offset-list 1 in 100000 fa0/0 (fa0/0) being the inbound interface receiving the redistributed OSPF routes, the off-set list works and the path is redirected to another router perform OSPF / EIGRP redistribution, as I wanted to.
My question is why is the path not influenced if I do NOT specify an inbound interface. I can clearly see the metric is incremented, however the path is unaffected.
Working Code:
R4#sh ip route 1.1.1.1
Routing entry for 1.1.1.1/32
Known via "eigrp 1", distance 170, metric 286720, type external
Redistributing via eigrp 1
Last update from 10.0.0.6 on FastEthernet0/1, 00:02:14 ago
Routing Descriptor Blocks:
* 10.0.0.6, from 10.0.0.6, 00:02:14 ago, via FastEthernet0/1
Route metric is 286720, traffic share count is 1
Total delay is 1200 microseconds, minimum bandwidth is 10000 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 2
R4#sh ip eigrp top
IP-EIGRP Topology Table for AS(1)/ID(10.0.0.9)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 1.1.1.1/32, 1 successors, FD is 286720
via 10.0.0.6 (286720/284160), FastEthernet0/1
via 10.0.0.10 (1284160/281600), FastEthernet0/0
Non-Working (excluding fa0/0 as the specified interface to apply an offset list to)
[PHP]
R4#sh runBuilding configuration...
Current configuration : 1080 bytes!version 12.4service timestamps debug datetime msecservice timestamps log datetime msecno service password-encryption!hostname R4!boot-start-markerboot-end-marker!!no aaa new-modelmemory-size iomem 10ip cef!!!!no ip domain lookupip domain name lab.local!multilink bundle-name authenticated!!!!!!!!!!!!!!!!!!!!!archive log config hidekeys!!!!!!!!interface FastEthernet0/0 ip address 10.0.0.9 255.255.255.252 duplex auto speed auto!interface Serial0/0 no ip address shutdown!interface FastEthernet0/1 ip address 10.0.0.5 255.255.255.252 duplex auto speed auto!interface Serial0/1 ip address 10.0.0.2 255.255.255.252!router eigrp 1 offset-list 1 in 1000000 network 10.0.0.0 no auto-summary!ip forward-protocol nd!!no ip http serverno ip http secure-server!access-list 1 permit 1.1.1.1!!!!!control-plane!!!!!!!!!!line con 0 exec-timeout 0 0 privilege level 15 logging synchronousline aux 0 exec-timeout 0 0 privilege level 15 logging synchronousline vty 0 4 login!!end
[/PHP]
R4#sh ip route 1.1.1.1
Routing entry for 1.1.1.1/32
Known via "eigrp 1", distance 170, metric 1284160, type external
Redistributing via eigrp 1
Last update from 10.0.0.10 on FastEthernet0/0, 00:00:02 ago
Routing Descriptor Blocks:
* 10.0.0.10, from 10.0.0.10, 00:00:02 ago, via FastEthernet0/0
Route metric is 1284160, traffic share count is 1
Total delay is 40162 microseconds, minimum bandwidth is 10000 Kbit
Reliability 1/255, minimum MTU 1500 bytes
Loading 255/255, Hops 1
IP-EIGRP Topology Table for AS(1)/ID(10.0.0.9)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 1.1.1.1/32, 1 successors, FD is 1284160
via 10.0.0.10 (1284160/281600), FastEthernet0/0
via 10.0.0.6 (1286720/284160), FastEthernet0/1
Thanks!
offset-list 1 in 100000 -- this command increments the metric of the network I am targeting with access-list 1. However it does NOT seem to influence the path.
Then when I enter the command:
offset-list 1 in 100000 fa0/0 (fa0/0) being the inbound interface receiving the redistributed OSPF routes, the off-set list works and the path is redirected to another router perform OSPF / EIGRP redistribution, as I wanted to.
My question is why is the path not influenced if I do NOT specify an inbound interface. I can clearly see the metric is incremented, however the path is unaffected.
Working Code:
R4#sh run Building configuration... Current configuration : 1096 bytes ! version 12.4 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname R4 ! boot-start-marker boot-end-marker ! ! no aaa new-model memory-size iomem 10 ip cef ! ! ! ! no ip domain lookup ip domain name lab.local ! multilink bundle-name authenticated ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! archive log config hidekeys ! ! ! ! ! ! ! ! interface FastEthernet0/0 ip address 10.0.0.9 255.255.255.252 duplex auto speed auto ! interface Serial0/0 no ip address shutdown ! interface FastEthernet0/1 ip address 10.0.0.5 255.255.255.252 duplex auto speed auto ! interface Serial0/1 ip address 10.0.0.2 255.255.255.252 ! router eigrp 1 offset-list 1 in 1000000 FastEthernet0/0 network 10.0.0.0 no auto-summary ! ip forward-protocol nd ! ! no ip http server no ip http secure-server ! access-list 1 permit 1.1.1.1 ! ! ! ! ! control-plane ! ! ! ! ! ! ! ! ! ! line con 0 exec-timeout 0 0 privilege level 15 logging synchronous line aux 0 exec-timeout 0 0 privilege level 15 logging synchronous line vty 0 4 login ! ! end
R4#sh ip route 1.1.1.1
Routing entry for 1.1.1.1/32
Known via "eigrp 1", distance 170, metric 286720, type external
Redistributing via eigrp 1
Last update from 10.0.0.6 on FastEthernet0/1, 00:02:14 ago
Routing Descriptor Blocks:
* 10.0.0.6, from 10.0.0.6, 00:02:14 ago, via FastEthernet0/1
Route metric is 286720, traffic share count is 1
Total delay is 1200 microseconds, minimum bandwidth is 10000 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 2
R4#sh ip eigrp top
IP-EIGRP Topology Table for AS(1)/ID(10.0.0.9)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 1.1.1.1/32, 1 successors, FD is 286720
via 10.0.0.6 (286720/284160), FastEthernet0/1
via 10.0.0.10 (1284160/281600), FastEthernet0/0
Non-Working (excluding fa0/0 as the specified interface to apply an offset list to)
[PHP]
R4#sh runBuilding configuration...
Current configuration : 1080 bytes!version 12.4service timestamps debug datetime msecservice timestamps log datetime msecno service password-encryption!hostname R4!boot-start-markerboot-end-marker!!no aaa new-modelmemory-size iomem 10ip cef!!!!no ip domain lookupip domain name lab.local!multilink bundle-name authenticated!!!!!!!!!!!!!!!!!!!!!archive log config hidekeys!!!!!!!!interface FastEthernet0/0 ip address 10.0.0.9 255.255.255.252 duplex auto speed auto!interface Serial0/0 no ip address shutdown!interface FastEthernet0/1 ip address 10.0.0.5 255.255.255.252 duplex auto speed auto!interface Serial0/1 ip address 10.0.0.2 255.255.255.252!router eigrp 1 offset-list 1 in 1000000 network 10.0.0.0 no auto-summary!ip forward-protocol nd!!no ip http serverno ip http secure-server!access-list 1 permit 1.1.1.1!!!!!control-plane!!!!!!!!!!line con 0 exec-timeout 0 0 privilege level 15 logging synchronousline aux 0 exec-timeout 0 0 privilege level 15 logging synchronousline vty 0 4 login!!end
[/PHP]
R4#sh ip route 1.1.1.1
Routing entry for 1.1.1.1/32
Known via "eigrp 1", distance 170, metric 1284160, type external
Redistributing via eigrp 1
Last update from 10.0.0.10 on FastEthernet0/0, 00:00:02 ago
Routing Descriptor Blocks:
* 10.0.0.10, from 10.0.0.10, 00:00:02 ago, via FastEthernet0/0
Route metric is 1284160, traffic share count is 1
Total delay is 40162 microseconds, minimum bandwidth is 10000 Kbit
Reliability 1/255, minimum MTU 1500 bytes
Loading 255/255, Hops 1
IP-EIGRP Topology Table for AS(1)/ID(10.0.0.9)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 1.1.1.1/32, 1 successors, FD is 1284160
via 10.0.0.10 (1284160/281600), FastEthernet0/0
via 10.0.0.6 (1286720/284160), FastEthernet0/1
Thanks!
Currently Studying: IE Stuff...kinda...for now...
My ultimate career goal: To climb to the top of the computer network industry food chain.
"Winning means you're willing to go longer, work harder, and give more than anyone else." - Vince Lombardi
My ultimate career goal: To climb to the top of the computer network industry food chain.
"Winning means you're willing to go longer, work harder, and give more than anyone else." - Vince Lombardi
Comments
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Danielh22185
Member Posts: 1,195 ■■■■□□□□□□
screwed something up there...
here is the config of when the offset list is applied without specifying the fa0/0 interface to apply it to:R4#sh runBuilding configuration... Current configuration : 1080 bytes ! version 12.4 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname R4 ! boot-start-marker boot-end-marker ! ! no aaa new-model memory-size iomem 10 ip cef ! ! ! ! no ip domain lookup ip domain name lab.local ! multilink bundle-name authenticated ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! archive log config hidekeys ! ! ! ! ! ! ! ! interface FastEthernet0/0 ip address 10.0.0.9 255.255.255.252 duplex auto speed auto ! interface Serial0/0 no ip address shutdown ! interface FastEthernet0/1 ip address 10.0.0.5 255.255.255.252 duplex auto speed auto ! interface Serial0/1 ip address 10.0.0.2 255.255.255.252 ! router eigrp 1 offset-list 1 in 1000000 network 10.0.0.0 no auto-summary ! ip forward-protocol nd ! ! no ip http server no ip http secure-server ! access-list 1 permit 1.1.1.1 ! ! ! ! ! control-plane ! ! ! ! ! ! ! ! ! ! line con 0 exec-timeout 0 0 privilege level 15 logging synchronous line aux 0 exec-timeout 0 0 privilege level 15 logging synchronous line vty 0 4 login ! ! end
Currently Studying: IE Stuff...kinda...for now...
My ultimate career goal: To climb to the top of the computer network industry food chain.
"Winning means you're willing to go longer, work harder, and give more than anyone else." - Vince Lombardi -
APA
Member Posts: 959
It looks like it has worked in your last snippet.
You don't specify a specific interface to pair the offset with. Therefore 'offset-list in' is 'offsetting' 1000000 to all eigrp interfaces in 10.0.0.0/8 where 1.1.1.1 is received. Therefore 10.0.0.10 is seen as the best next hop still due to the FD of 1284160.
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Danielh22185
Member Posts: 1,195 ■■■■□□□□□□
It looks like it has worked in your last snippet.
You don't specify a specific interface to pair the offset with. Therefore 'offset-list in' is 'offsetting' 1000000 to all eigrp interfaces in 10.0.0.0/8 where 1.1.1.1 is received. Therefore 10.0.0.10 is seen as the best next hop still due to the FD of 1284160.
Ah ha! Thank you! That makes perfect sense why I would not see a path change then, essentially I am increasing all metric to that route.Currently Studying: IE Stuff...kinda...for now...
My ultimate career goal: To climb to the top of the computer network industry food chain.
"Winning means you're willing to go longer, work harder, and give more than anyone else." - Vince Lombardi -
APA
Member Posts: 959
No problems
Always helps to have another pair of eyes looks over the outputs.
CCNA | CCNA:Security | CCNP | CCIP
JNCIA:JUNOS | JNCIA:EX | JNCIS:ENT | JNCIS:SEC
JNCIS:SP | JNCIP:SP