Administrative Distance for CCNA students

[lagapidis (Lazarus Agapidis)]

Hello Marit

@maritdelange

Who has determined those administrative distances

Administrative distances are indeed assigned by the vendor, and the values you see in the lesson are values assigned by Cisco. This does make sense when you see that EIGRP is given a better AD that OSPF. Although they are assigned by vendors, they are not entirely based on preference of the proprietary over the open architecture protocols. The default ADs are specifically chosen to ensure an optimum functionality under the most common circumstances.

@maritdelange

So how does this work when there is a non-Cisco router in the network, do these ADs still play a role or are they only relevant in a network with solely Cisco routers?

Other vendors use AD values as well, but the interoperation of routers from various vendors are not that much of an issue because the AD is local to the router and is not something that is shared in any routing updates. However, it is of utmost importance that the ADs on routers within the same routing domain be the same. Otherwise, routing loops and black holes may arise.

@maritdelange

I find this confusing. I’ve heard non-cisco network engineers (engineers who are not cisco certified) saying that OSPF is better. My IT-teacher for example, who was a network engineer for many years and taught me a networking-unit, did not want to teach us about EIGRP as he said it was obsolete.

Like in many disciplines, professionals become attached to specific protocols and methodologies because they have experience with them. I too am not immune to this. . To be fair, both EIGRP and OSPF are exceptional protocols and I have seen both be implemented successfully in many large networks. The truth is that each has its strengths and weaknesses for specific situations. I stated that EIGRP was better than OSPF, at least as far as convergence goes, because it has the feasible successor built in which provides exceptional convergence speed. OSPF on the other hand is better in scalability due to the fact that you can separate a network into somewhat autonomous areas. So it really depends on what your requirements are.

Now Cisco has chosen to place EIGRP above OSPF, which is a design choice, which may indeed be influenced by the fact that it is proprietary, but it is based on valid technological research as well.

(But to go as far as to say that EIGRP is obsolete, in my opinion, simply shows contempt rather than rational thought.)

Just for argument’s sake, EIGRP has now been opened to be freely used by other vendors as well, and vendors such as HP for example, are indeed using it in their equipment. It is described in the IETF RFC 7868.

I hope this has been helpful!

Laz