CRC errors on cable modem connection

[hegleran]

Well first I'd like to say hi as I'm new to this forum. I did some poking around and couldn't find a thread already dealing with this issue, so I apologize if there is something floating out there already. I recently set up a cisco 1751 behind my cable modem. From there I am running a 3com superstack II 3300 to my pcs. The interface running to my cable modem is a wic 1enet. On it (e1/0), I am getting tons of CRC and input errors:

Last clearing of "show interface" counters 00:18:07
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue :0/40 (size/max)
5 minute input rate 246000 bits/sec, 116 packets/sec
5 minute output rate 297000 bits/sec, 34 packets/sec
133224 packets input, 34875556 bytes, 0 no buffer
Received 84724 broadcasts, 0 runts, 3 giants, 0 throttles
1710 input errors, 972 CRC, 735 frame, 0 overrun, 0 ignored
0 input packets with dribble condition detected
44797 packets output, 41973532 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier
0 output buffer failures, 0 output buffers swapped out

Is this normal for cable modem connections, due to signal strength etc?
I'm used to frame-relay circuits at work that tend to run very clean, so this is why I'm a bit concerned.
fa0/0 is clean, which is the interface running to my switch.

Here's my config for those interested (I still need to build my acls)
:
Building configuration...

Current configuration : 1261 bytes
!
version 12.2
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname 1751v
!
enable secret 5 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
!
memory-size iomem 15
ip subnet-zero
!
!
ip dhcp excluded-address 192.168.1.254
ip dhcp excluded-address 192.168.1.252 255.255.255.0
!
ip dhcp pool insideDHCP
network 192.168.1.0 255.255.255.0
default-router 192.168.1.254
dns-server xxxxxxxxxxxxxxxxxxxxx
!
!
!
voice call carrier capacity active
!
!
!
!
!
!
!
!
!
mta receive maximum-recipients 0
!
!
!
interface FastEthernet0/0
ip address 192.168.1.254 255.255.255.0
ip nat inside
no ip route-cache
no ip mroute-cache
speed auto
!
interface Serial0/0
no ip address
shutdown
!
interface Ethernet1/0
ip address dhcp
ip nat outside
no ip route-cache
no ip mroute-cache
full-duplex
!
ip nat inside source list 1 interface Ethernet1/0 overload
ip classless
no ip http server
!
!
access-list 1 permit 192.168.1.0 0.0.0.255
!
call rsvp-sync
!
voice-port 2/0
!
voice-port 2/1
!
!
mgcp profile default
!
dial-peer cor custom
!
!
!
banner motd ^CAuthorized Access Only^C
!
line con 0
exec-timeout 0 0
password xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
logging synchronous
login
line aux 0
line vty 0 4
password xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
login
!
end


Any help would be greatly appreciated in figuring out all of these nasty errors piling up.

Thanks,
-Andy

 

[hegleran]

I should also mention - my cable modem performance "feels" about average right now. Not stellar, but it's certainly functional.

 

[JOAMON]

It looks to be a speed/duplex problem. The 1751 WIC-1ENET is only cabaple of 10 full duplex. Some devices have problems communicating with this speed and duplex type. You can try a couple of things and choose the best. 1 would be to put a small auto negotiating switch between the modem and router. Clear the counters and monitor for further errors. 2 you could change the duplex on e1/0 to half clear the counters and monitor for errors. This setting should see the CRC errors go away but you will start getting collisions (Not the better choice). 3 you could switch the interfacce roles and put the fast ethernet on the cable modem side and the e1/0 on the lan side. Should not see a speed problem as your bottleneck will be the cable and not the 10 speed ethernet port.

 

[hegleran]

Joamon,

I appreciate all of your feedback. I am going to have to throw away option 3, as I do use the lan side of the network considerably for streaming music, data transfer and backup, etc. I don't want to drop that network down to 10Mbps. I may be running into a cisco 2900 for free, if that is the case, I can put the 3com between the cable modem and router, and then use the cisco on the lan. Talk about a waste of resources though!

Here's an idea, although I'm not sure if it is possible:
If I set up to two vlans on the switch, one for the lan... say for ports 1-22, and 1 for the cable connection, ports 23,24; could I run vlan 1 into the fast ethernet interface of the router, and vlan2 into the wic1 enet interface?
This way I'd have my two networks, both on the autosensing switch, without the need for another physical switch. The only thing I'm questioning is, would I need to assign vlan 2 (the wan vlan) an ip...because if so, since I'm getting my ip from the isp via dhcp, and my isp only gives me 1 global address, I might be stuck, as I'd need an address for the router and vlan2 on the switch...
I suppose also, this router would have to be able to function as a router-on-a-stick to be able to route between the two vlans, however I've never dealt with a configuration that vlans coming from more than 1 interface. I don't know, that sounds awfully complicated for what I'm trying to accomplish here...

I suppose for the time being though, I can just live with the errors, since, as I've mentioned, performance seems about normal. I really wish I had another fast ethernet interface on the router. Maybe I can trade this in for something a little more suitable, as I have no use for the voice card, or the t1 csu/dsu card.

Thanks again for your recommendations, and any further insight would be appreciated as well.

 

[JOAMON]

Tak a look on EBay. There are several Cisco 2621 routers available starting at $260.00. This router has two built-in fast ethernet ports, 2-WIC slots, and 1 NM slot. Keep the T1 wic as you may want to upgrade to T1 internet someday. You could then probably sell the 1700 on EBay and recover 2/3 of the cost or keep it as a cold spare.

 

[JOAMON]

Make sure to get one with 64/16 memory if you choose to go that way.

 

[JOAMON]

If that is a voice capable router they go for a pretty good price on EBay. If it has the FXS or FXO wic and the PVDM (packet voice data module) installed. A show version should reveal this information. Not sure but seem to recall that there is also an PVDM indicator light on the back that when lit there is a module present.

 

[JOAMON]

Another reason to keep the T1 card would be for a point to point connection to another office.

 

[JOAMON]

Try getting a $30 auto-sensing auto-negotiating 10/100 switch and put between the two devices.

 

[hegleran]

Well, I won't be switching to a T1 at anytime, as this is for home use, and I have a 4Mbps connection at home. The easiest solution would be to buy a cheap small switch to throw in between the two devices, however, I may wind up looking for a 2621 to replace this with as that would be the cleanest fix.

Thanks again for your help!

 

[JOAMON]

Can you post the output from a show version when you get a chance?

 

[hegleran]

Sure thing, I'm not at home right now, but I will this evening.

 

[hegleran]

1751v#sh ver
Cisco Internetwork Operating System Software
IOS (tm) C1700 Software (C1700-SV8Y-M), Version 12.2(11)T, RELEASE SOFTWARE (fc
1)
TAC Support:

http://www.cisco.com/tac

Copyright (c) 1986-2002 by cisco Systems, Inc.
Compiled Wed 31-Jul-02 09:56 by ccai
Image text-base: 0x80008124, data-base: 0x8112C9B0

ROM: System Bootstrap, Version 12.2(1r)XE1, RELEASE SOFTWARE (fc1)

1751v uptime is 0 minutes
System returned to ROM by power-on
System image file is "flash:c1700-sv8y-mz.122-11.T.bin"

cisco 1751 (MPC860P) processor (revision 0x200) with 55706K/9830K bytes of memor
y.
Processor board ID JAD063305ZE (655151708), with hardware revision 0000
MPC860P processor: part number 5, mask 2
Bridging software.
X.25 software, Version 3.0.0.
1 Ethernet/IEEE 802.3 interface(s)
1 FastEthernet/IEEE 802.3 interface(s)
1 Serial network interface(s)
2 Voice FXO interface(s)
WIC T1-DSU
32K bytes of non-volatile configuration memory.
32768K bytes of processor board System flash (Read/Write)

Configuration register is 0x2102

 

[JOAMON]

Does not look like there is a PVDM module in this router but with the interface cards you have if you were to but a 2621 you should be able to recover most of it by selling this router. I would try the cheap switch first though.