Hey Marc, To emphasise, this is for the 33.33.33.33 loopback, or Cat3 loopback route.
I see: R2-R5-Cat3 R2-R6-Cat4-Cat3 R2-R4-Cat1-Cat3 Why would i go through Cat2 ? So in my count it should prefer the route through R5? On Jul 12, 2011, at 11:05 PM, marc abel wrote: > You can see they all have an equal cost [110/66] of 66. Looking at > your diagram I see > > R2-R4-Cat1-Cat2-Cat2 loopback > R2-R5-Cat3-Cat2-Cat2 loopback > R2-R6-Cat4-Cat2-Cat2 loopback > > Extra fiddling is one of the best ways to learn this stuff. > > On Tue, Jul 12, 2011 at 4:49 PM, Alef <[email protected]> wrote: >> Thanks Marc. >> >> This was the problem: >> R6#sh class-map type inspect >> Class Map type inspect match-any corporate-to-private-class (id 1) >> Match protocol telnet >> Match protocol ssh >> Match protocol ftp >> >> Once i added icmp all was well. I didn't actually expect the route to go >> over that for some reason, nor do i understand why it had r6 in it's path >> with equal distance, as there is at least one more l3 switch in between >> compared to R5. Same for R4. Does it not see the "switches" as a hop or >> something ? >> O 33.33.33.33 [110/66] via 100.100.100.6, 00:13:27, Serial1/1.256 >> [110/66] via 100.100.100.5, 00:13:27, Serial1/1.256 >> [110/66] via 100.100.24.4, 00:07:08, Serial1/0.24 >> >> This is what i get for fiddling with labs designed for a different purpose >> and then trying to add more functionality (or get more out of it) ;-) >> >> >> On Jul 12, 2011, at 10:36 PM, marc abel wrote: >> >>> Layer 2 loops are caused because switches by default flood traffic out >>> all ports, so any time you connect switches in a circular path a loop >>> would form if not for spanning-tree. >>> >>> In layer 3 this is not the case. Since you have to specifically tell >>> traffic where to route, making a circle does not make a loop. Routes >>> make loops by referring back to a host that thinks its path is back to >>> itself. So adding layer 3 interfaces is not the cause of the loops, >>> incorrect routes are. >>> >>> Take this example >>> >>> R1. >>> int g0/0 >>> ip address 10.10.10.1 255.255.255.0 >>> no shut >>> ! >>> ip route 6.6.6.6 255.255.255.255 10.10.10.2 >>> >>> R2. >>> int g0/0 >>> ip address 10.10.10.2 255.255.255.0 >>> no shut >>> ! >>> ip route 6.6.6.6 255.255.255.255 10.10.10.1 >>> >>> >>> Now try to traceroute to 6.6.6.6. R1 will send it to R2, R2 will send >>> it to R1, R1 will send to R2, repeat until the TTL expires. This is a >>> layer 3 loop. You will generally notice layer 3 loops by traffic not >>> reaching its destination(and proved by traceroute), or by routes being >>> repeatedly installed and removed from the routing table (debug ip >>> routing). >>> >>> Layer 2 loops will generally either keep looping the traffic around so >>> much that you lose access to the device and the whole damn network >>> crashes, or if you are lucky you might not have it so bad and you will >>> see a message in the logs that says something like host x.x.x.x is >>> flapping between interface..... >>> >>> -Marc >>> >>> >>> >>> >>> On Tue, Jul 12, 2011 at 3:37 PM, Alef <[email protected]> wrote: >>>> No no redistribution. I tried to keep it as simple as possible. >>>> Ok let me try my hand at some ascii art. >>>> >>>> But before i do that, is there some inherent stupid thing about putting >>>> vlan interfaces in all the vlans on all the switches ( i have dot1q trunks >>>> in x between all 4 switches). I can imagine in my network it would create >>>> a loop. Just a hunch if i follow the paths. Would i not automatically >>>> introduce L3 loops by doing that. I think ipexpert topology is setup >>>> similar ? >>>> >>>> ok scratch that, i uploaded a small jpg >>>> http://tinypic.com/r/fkqfqr/7 >>>> >>>> All switches loopbacks are reachable by at least 3 paths (2 trough the FR >>>> cloud, and 1 other) >>>> >>>> R2# >>>> O 11.11.11.11 [110/66] via 100.100.100.6, 01:01:51, Serial1/1.256 >>>> [110/66] via 100.100.100.5, 01:01:51, Serial1/1.256 >>>> [110/66] via 100.100.24.4, 00:00:43, Serial1/0.24 >>>> 44.0.0.0/32 is subnetted, 1 subnets >>>> O 44.44.44.44 [110/66] via 100.100.100.6, 01:01:51, Serial1/1.256 >>>> [110/66] via 100.100.100.5, 01:01:51, Serial1/1.256 >>>> [110/66] via 100.100.24.4, 00:00:43, Serial1/0.24 >>>> >>>> On a probably unrelated side note, anyone ever got : >>>> %OSPF-4-ERRRCV: Received invalid packet: Bad Checksum from 100.100.14.1, >>>> Vlan14 >>>> >>>> Cisco website says change the port or cable, which i did, and cable, well >>>> considering it's a dynamips sim i did that as best as i could :-) >>>> >>>> Can't get the message to go away though. >>>> >>>> On Jul 12, 2011, at 5:24 PM, Di Bias, Steve wrote: >>>> >>>>> >>>>> What makes you think you have any kind of loop? What are the symptoms? >>>>> Are you redistributing anywhere? >>>>> >>>>> -----Original Message----- >>>>> From: [email protected] >>>>> [mailto:[email protected]] On Behalf Of Alef >>>>> Sent: Tuesday, July 12, 2011 8:27 AM >>>>> To: [email protected] IE >>>>> Subject: [OSL | CCIE_RS] loop in network? >>>>> >>>>> All, >>>>> >>>>> So i have this network, and i am thinking i have a loop. I'm just not >>>>> sure where or how. >>>>> And i think it started happening after i created vlan interfaces in all >>>>> vlans on all switches. So Cat1 is having vlan14,vlan567 and vlan69 >>>>> interfaces and all the other switches in similar. >>>>> >>>>> They are NM16ESW cards, but IEEE stp is running so a Layer2 loop should >>>>> be out of the question. Could i still have a routing loop? >>>>> I am running OSPF in one giant area 0. >>>>> >>>>> How would i go about solving it? I can't use split horizon as OSPF >>>>> doesn't use that. Should i artificially set routes such that they get a >>>>> lower metric and manipulate things like that? >>>>> >>>>> I attached a small picture to clarify (this is taken from the Security >>>>> lab Day4 VoD btw). >>>>> Mind you, it might be something different entirely although i don't think >>>>> so. >>>>> >>>>> But it's probably going to be something very stupid. And yes, i probably >>>>> don't understand switching very well yet :-) >>>>> >>>>> Alef >>>>> >>>>> >>>>> UHS Confidentiality Notice: This e-mail message, including any >>>>> attachments, is for the sole use of the intended recipient (s) and may >>>>> contain confidential and privileged information. Any unauthorized >>>>> review, use, disclosure or distribution of this information is >>>>> prohibited. If this was sent to you in error, please notify the sender >>>>> by reply e-mail and destroy all copies of the original message. >>>> >>>> _______________________________________________ >>>> For more information regarding industry leading CCIE Lab training, please >>>> visit www.ipexpert.com >>>> >>>> Are you a CCNP or CCIE and looking for a job? Check out >>>> www.PlatinumPlacement.com >>>> >> >> _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com
