Administrative distance in Cisco proprietary protocols

[j.sivasankar92]

Hello to all professionals,
                       
                        Default AD value for following,
   
Rip- 120
OSPF- 110
EIGRP-90

Then why we have the distance changing value options.

Like following when we enabled the protocols,

router(config-router)#distance ?

[deanwebb]

The options are for route tuning, to prefer certain routes over others.

[j.sivasankar92]

Oh! ok for Rip protocol default AD is 120 if I'm going to reduce as a 60.
60 is least than others. I meant that has a lowest AD value.
So it will be a prefer than others. I got it.
But there is any limitations to reduce upto ...I'm asking any limit range is there for to reduce on each protocols.

[srg]

The range is from 0 to 255.

[NetworkGroover]

Hello to all professionals,
                       
                        Default AD value for following,
   
Rip- 120
OSPF- 110
EIGRP-90

Then why we have the distance changing value options.

Like following when we enabled the protocols,

router(config-router)#distance ?

There are some special case scenarios where you may need or want to do it.  It's a tool in the toolbox, basically. One that comes to mind that I did somewhat recently was modifying AD for iBGP and eBGP for a mutual redistribution scenario involving two vendors.

[Reggle]

Another example is in a network where I'd like a third party EIGRP preferred over my own OSPF. All nice with default AD values (90 and 110) until the third party redistributed static routes, with come in as EIGRP External at... AD 170. Distance 180 for OSPF and it's solved.

[NetworkGroover]

Another example is in a network where I'd like a third party EIGRP preferred over my own OSPF. All nice with default AD values (90 and 110) until the third party redistributed static routes, with come in as EIGRP External at... AD 170. Distance 180 for OSPF and it's solved.

That's a good one.

I'd also like to add a little more context to the example I provided for the OP.  Sometimes vendors don't agree on what ADs should be for certain things, so when you have multivendor environments that's where you might often do things like modify AD, STP costs, etc. where you usually wouldn't in a single vendor environment.