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 Post subject: Serial interfaces going down/down often
PostPosted: Thu Jan 20, 2011 12:14 pm 
I am seeing problems whereby various actions cause serial interfaces to go down/down, sometimes they come back on their own and sometimes I have to shut/no shut to get them back - this is incredibly frustrating as often I will be trying to make something work, and have to go searching to see if connectivity is there or if my config is broken.

if a router sends a crypto packet, or perhaps a TACACS start packet, these are the types of things which seem to bring down the frame interfaces.

running 2691's with 124-15.T12

the GNS3 version is 0.6 running on Ubunutu, CPU load is about 80% on each of the 4 cores. Memory is plenty free.

here is example problem config;

!
interface Serial0/0
no ip address
encapsulation frame-relay
frame-relay lmi-type ansi
!
interface Serial0/0.345 point-to-point
ip address 183.1.0.4 255.255.255.0
ip nat outside
ip virtual-reassembly
ip ospf network point-to-multipoint
snmp trap link-status
frame-relay interface-dlci 405
crypto map CRYPTO
!


and I have a FRSW in GNS3;

[[FRSW FRSW]]
1:102 = 2:201
1:103 = 3:301




I seem to remember something about having to configure serial interfaces differrently in GNS3 to the real world, can anyone please point me in the right direction?




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 Post subject: Re: Serial interfaces going down/down often
PostPosted: Thu Jan 20, 2011 7:07 pm 
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Joined: Fri Mar 05, 2010 11:33 am
Posts: 1494
Location: Australia
Your problem is almost certainly related to a lack of resources. Things to try:
1. Get a better idle-pc value. See The Illusive Art of Acquiring A Good Idle-PC Value
2. Try and use the same router model for all router instances, and the same image, and make sure Enable ghost IOS support is enabled under Preferences->Dynamips
3. Try reducing the amount of RAM used by your router - although this may lead to stability problems.
4. Use a better PC or better OS - I find GNS3 works much better on OSX than an equivalent Windows PC

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GNS3 WorkBench-a VMware image of Ubuntu with GNS3 and VPCS installed and a collection of exercises/labs


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 Post subject: Re: Serial interfaces going down/down often
PostPosted: Sat Jan 22, 2011 11:52 am 
I have played more with idle-pc, and I now have:

9 routers running, all 2621XM with Advanced Security 12.4(15)T14
2 PIX with 8.03
2 virtual machines in virtual box

my CPU is less than 30%, and I have more than 3GB of free RAM.

ghost IOS option doesnt seem to help either way

RAM in each 2621XM is the min needed by the image, 192MB


anyone have any other ideas?


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 Post subject: Re: Serial interfaces going down/down often
PostPosted: Sat Jan 22, 2011 1:47 pm 
even when stopping some instances so I only have 5 routers running, this still happens.

I have also replaced the GNS3 frame-relay switch with a router instance acting as the frame switch, and still have the problem.....


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 Post subject: Re: Serial interfaces going down/down often
PostPosted: Mon Jan 24, 2011 10:29 am 
I have spent more time on troubleshooting this, and have made it better but not fixed.

I have put each router into it's own dynamips hypervisor instance, and things are better. But when switching on my physical switches (trunked into GNS3) and BGP comes up over ethernet, things start to go awry again, even though CPU is only at 30%. Thankfully I don really need BGP to study security, and if I need the routes I'll just static them!

I dont know why the routers struggle though, when host CPU is ~30% and none of the dynamips instances are maxing out a single core.


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 Post subject: Re: Serial interfaces going down/down often
PostPosted: Thu Feb 10, 2011 11:49 pm 
I changed IOS images, and everything is ok for now, running 10 routers and a couple of VM's in a 32-bit Fedora 14, and so far so good.

incidentally I ditched gns3 and just use dynagen CLI


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 Post subject: Re: Serial interfaces going down/down often
PostPosted: Wed May 18, 2011 5:30 pm 
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Joined: Wed May 18, 2011 5:18 pm
Posts: 3
i had the serial interface flapping problem, and it was due to the high CPU utilization. all i did was switched from the 2691 image to a 3640 one.

i just ran 6 routers with BGP. CPU was below 20% all the time....!!! neighborships were up and routes propagated.

i used a Intel core 2 duo with 2 GB RAM. the laptop was a Dell Vistro 1220 running Windows 7.
IOS image was c3640-jk9s-mz.124-16a.bin and i decompressed and used it. i booted each router one at a time, but it only took around 3-4 minutes to get all 5 BGP routers up and running smoothly. (from loading the GNS3 application to checking the "show ip bgp" command output with learned routes from the other end)




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