auto summarization…

why this lingers…

for the ccie lab exam this is the ios guidance… https://learningnetwork.cisco.com/docs/DOC-5249

Version 4.0
  • 1841 series routers – IOS 12.4(T) – Advanced Enterprise Services
  • 3825 series routers – IOS 12.4(T) – Advanced Enterprise Services
  • Catalyst 3560 Series switches running IOS version 12.2 – Advanced IP Services

note the version of ios on one of my 3560’s below:

dsw1#sh ver                                                                      
Cisco IOS Software, C3560 Software (C3560-IPSERVICESK9-M), Version 12.2(55)SE6,
note the default behavior behavior of eigrp:

dsw1#sh run | b router                                                           
router eigrp 10                                                                  
 network 4.4.4.0 0.0.0.255                                                       
 network 10.1.4.0 0.0.0.255                                                      
 network 10.2.0.0 0.0.255.255                                                    
 network 192.168.1.0

if you’ve used ios for more than 11 seconds you’ll know that default settings often do not show up in the output of sh run…

dsw1(config)#router eigrp 10                                                     
dsw1(config-router)#auto-summ                                                    
dsw1(config-router)#                                                             
.Feb 23 08:24:08: %DUAL-5-NBRCHANGE: EIGRP-IPv4 10: Neighbor 10.1.4.5 (FastEtherd
.Feb 23 08:24:08: %DUAL-5-NBRCHANGE: EIGRP-IPv4 10: Neighbor 192.168.1.130 (Vland
.Feb 23 08:24:08: %DUAL-5-NBRCHANGE: EIGRP-IPv4 10: Neighbor 10.2.1.2 (Vlan10) id

see how nice that worked out…

router eigrp 10                                                                  
 network 4.4.4.0 0.0.0.255                                                       
 network 10.1.4.0 0.0.0.255                                                      
 network 10.2.0.0 0.0.255.255                                                    
 network 192.168.1.0                                                             
 auto-summary  

now it shows up because the default is no auto-summary and has been for quite some time…

so in post-modern networking we shouldn’t have to be concerned about this nightmare, right?

wrong… it is hard to conceive in the vlsm era that someone would actually change the default of no auto-summary to auto-summary… the caveat here is suppose you were working on an older version of code, and auto-summary was on by default on one of the routers in the topology and, and, ad nauseum…

yeah, so you gotta know what the table output is going to look like in the event that this silly thing is on somewhere… that’s because ccna always looms in the shadows… 2 steps forward, five steps back…

this is the world we’ve chosen, so suck it up…

it’s war and you have to know the personal battles that must be lost along the way…

that it’s silly is not an option…

here is a great little article by greg ferro to help in your trip down memory lane…

http://etherealmind.com/eigrp-auto-summary-review/