loopback on ospf

[chinkevi_2]

hi all,

just a simple question but i can't find definate answer on.

in an OSPF network with multiple areas, is there a need to advertise loopback addresses (RID)?  Can the OSPF network works without having the need to advertise it? 

my thought is because RID is carried in the LSA, and there is no network reachability required to the loopback, i don't think loopback is required to be advertised.

there is no requirement for any router to use loopback for any management function like ntp/snmp/syslog,

thanks and regards

[Marwan ALshawi · Accepted solution]

First of all loopback used with ospf as rid is best practice but not must if there is no lo interface ospf will pickup one of physical ips

And yes u do not need to advertise the rid ip buy why u don't want ?

Loopback used for management ntp and other service as it is always up and if u advertise it through different interface it can be useful interim of alternate path for HA

Wish this help

If helpful rate

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[Marwan ALshawi]

First of all loopback used with ospf as rid is best practice but not must if there is no lo interface ospf will pickup one of physical ips

And yes u do not need to advertise the rid ip buy why u don't want ?

Loopback used for management ntp and other service as it is always up and if u advertise it through different interface it can be useful interim of alternate path for HA

Wish this help

If helpful rate

Sent from Cisco Technical Support iPhone App

[chinkevi_2]

thanks for the response..

all devices have dedicated physical interface for mgmt traffic like ntp and snmp, and no other interface is to used for mgmt traffic.

Loopback will only be used for RID and not require network reachability, it makes more sense not to advertise loopback in this case, isn't it?

[Thotsaphon Lueangwattanaphong · Accepted solution]

Hi,

   You don't need to advertise any IP address used for router-id but you can if you want to. That's why you can use a "router-id a.b.c.d" command and yes a.b.c.d doesn't have to be any ip address assigned on the router. In case you don't want to use a "router-id" command you're recommended to create loopback interface to be more stable than other interfaces(may be up or down) . And you don't need to advertise loopback's ip address in OSPF domain but you can if you want to. Keep in mind, "Router ID - A 32-bit number assigned to each router running the OSPF protocol. This number uniquely identifies the router within an Autonomous System"

HTH,

Toshi

[chinkevi_2]

thanks all for the response, they are helpful.