Cisco Switching/Routing :: 1841 Router Taking On ARP Table Entry
Dec 22, 2011
The issue is occuring on our local LAN where my ARP requests are being modified after a period of time by the router for one host. I'm finding that the host will work fine with the correct MAC IP pairing for a period of time and then about 15-30 minutes later, the arp table is changing so the associated mac/IP address is now the mac address of the router interface.
The FastEthernet 0/1 port has no ip proxy-arp enabled and is set with ip nat inside.This only started happening after restarting the router, however the running config was saved as the startup config prior to the restart.I've tried hard-coding the entry with the command arp 10.15.4.190 c82a.1459.0579 ARPA however that is not working as expected.
The device is an 1841 ISR with the advanced IP Services bundle loaded. Is there some way that the router is viewing my host (provides DNS, Directory Services) as a intrustion attempt and somehow rejecting the packets?
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Jan 23, 2011
I need to remove (or change) the default entry in the routing table for Windows XP, which routes packets with a destination equal to the adapter's address to localhost. The reason for this is I want the PC to be able to send packets to a device (with IP address A) connected to one adapter on the PC with IP address B, even though a second adapter on the PC has IP address A.
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Oct 7, 2012
I configure HSRP on Router 2951 as a primary router, and Router 2811 as backup router. But when I am switching off my Primary router the backup router is taking 2 mins to take over form primary router.
[code]....
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Nov 14, 2012
We have small which I'm looking to implement and have built this on GNS3.
We have:
Router A in site 1
Router B in site 2
Router C in site 3
Router A and B are connection via a point to point 100M link and from Router C we have a 2 point to point one of which is 5Mpbs and going to Router A and Router B.
For Router C to reach Router A network it will go via Router B and these are 100M connection. When the link between Router A and B goes down. Router C should update and start using the 5m route.
For some reson, the routes are not updating. I have to do 'clea ip eigrp ne' for the routes to update and if I reload the routers all works well, it seems the problem is intermittent.
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Mar 18, 2013
I am taking only undersize errors on catalyst 3750 trunk interface (attached some outputs)...the other end is a 4500 switch and the interface is clean..can this be related to any bug ? this is my root port and often leading to trouble sometimes STP BPDUs transportation are affected..
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Sep 25, 2012
We have a site and on that site we have a server which is down form last two days. However , to manage these devices we are not using any tools. We are not able to find this server that where it is located and on which switch it is connected to.
I want to know that the timer for mac address is 5 minutes and arp timeout is 4 hours . Is there any way to find out the mac address of the server . I feel like this can we done with cef ? Is it true or not I am not sure. I am running 3750 stacks and 2811 routers. 3750 stacks are working as layer 3 devices. They are also running the pretty new IOS 12.2(53)SE.
According to my understanding now a days CEF entry does not expire if we are not using them. They remain in cache as we are running with destination base CEF.
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Dec 3, 2012
We have a pair of 6509's with duplicate ACL lists & entries.
1 = Version 12.2(33)SXI4a
2 = Version 12.2(18)SXF15a
I wanted to remove some logging that was on an entry on one of our extended ACL's. On 1 this worked fine with the no 400
400 <acl rule without log>
However on 2 it lets me carry out the no 400 command but when i go to add the 400 <acl rule without log> i get the error % Duplicate sequence number.sure enough when i perform the 'Show access-lists <Name>' it is still there!
I have tried the following:
Adding a duplicate ACL entry before it (399) without log and i still get hits on line 400Adding and removing the duplicate created line 399 (without logging) with no issues.Adding and removing a dupliacte ACL (without Logging) after (line 401) with no issues
It looks like it is just this line it seems to think it has removed but hasn't?!
I understand an option is to duplicate the ACL in a text editor remove line, delete the ACL and put the edit back in .....however i wondered if this is something known (bug).
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Aug 19, 2011
Does PBR with deny ACL entries on a 3750 are still punted to the CPU? I found this article: URL
High CPU Due to Policy Based RoutingPolicy Based Routing (PBR) implementation in Cisco Catalyst 3750 switches has some limitations. If these restrictions are not followed, it can cause high CPU utilization. You can enable PBR on a routed port or an SVI. The switch does not support route-map deny statements for PBR. Multicast traffic is not policy-routed. PBR applies only to unicast traffic. Do not match ACLs that permit packets destined for a local address. PBR forwards these packets, which can cause ping or Telnet failure or route protocol flapping.
Do not match ACLs with deny ACEs. Packets that match a deny ACE are sent to the CPU, which can cause high CPU utilization.
In order to use PBR, you must first enable the routing template with the sdm prefer routing global configuration command. PBR is not supported with the VLAN or default template
I checked the latest config guide, and those same guidelines are still listed. If that limitation is still there, are those packets switched at the process level (ip_input) or the interrupt level?
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Jan 16, 2013
In datasheet of WS-SUP720-3B - link- was said that are only supported around 256K routes (fib?rib?).With this value I can't get 2 full bgp - that is around 850K ..
The supervisor is that control this or just memory ? I said this because I have a 7204-npe-g1 whith 2 fullrouting and 1G of and he are ok..
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Dec 26, 2011
I plugged an IP device into a 2960 Catalyst switch. The port is up, but there is no MAC address learned on it:
TNSWAGCS01002(config-if)#do sh mac add int fa0/16
Mac Address Table
-------------------------------------------
Vlan Mac Address Type Ports
---- ----------- -------- -----
TNSWAGCS01002(config-if)#
TNSWAGCS01002(config-if)#do sh int fa0/16
FastEthernet0/16 is up, line protocol is up (connected)
Hardware is Fast Ethernet, address is 0064.40ee.f510 (bia 0064.40ee.f510)
Description: --- STC ---
[code]....
I read that it may be a L1/L2 issue. We tried with another ethernet cable. We also tried with another IP device of the same model. That did not solve the issue.
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Dec 4, 2011
I have some error messages in the Nexus 7000 log, after searching i cannot find an adequate explanation, pretty much the only thing i can find is below and i don’t think it is very relevant to my situation. The device is in production and so reloading and pulling card willy nilly is the last resort.
Device = Nexus 7018
IOS version = 5.1(2)
Log messages=
2011 Dec 2 14:52:35 IAS01LVSWIPC01 %OC_USD-SLOT8-2-RF_CRC: OC2 received packets with CRC error from MOD 6 through XBAR slot 1/inst 1 and slot 2/inst 1 and slot 3/inst 1
[code]....
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Oct 30, 2011
I have configured a new switch 3560 switch and connected to 4500 switch and formed a trunk connectivity.Now the issue i am facing is when i do a SH CDP NEIGHBOUR from 3560 switch i am able so see 4500 swries switch but at the same time when i do SH CDP NEIGHBOUR form 4500 series switch i am not able to see the entry for 3560 switch.But i am able to telnet the new switch with out any issues
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Feb 2, 2009
Is there any way to clear a single ARP cache entry on the 6500 switch ?
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May 23, 2012
I have seen other discussions regarding Static MAC address entries on IPv4, but what of IPv6?We have MS NLB solutions and they are working fine. We have Cisco 6509/6504, Version 12.2(33)SXI5
But then we have a new one for a new ActiveDirectory solution, and on those networks we have implemented IPv6.
How is Static MAC address entries and MS NLB solved in IPv6 (i.e arp ip.ip.ip.ip mac.mac.mac ARPA gi1/1). I can't seem to find much examples or documentation on this? Is it replaced with another function?The reason I ask is twofold.
1. I really want to know
2. The NLB cluster seem to drop IPv6 traffic at even intervals, witch seems to correspond with NLB transition.
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Nov 3, 2011
In my lab, there are some machines that are connected using Cisco 2950 switches. Those machines belong to a VLAN.Now I need to modify the VLAN settings of the machines and as such I also need to modify the VLAN settings on the ports on the Cisco switches.
In order to do this, first I need to login to those switches, but due to a lack of knowledge transfer, I don't have the password. Is the some generic password?Second I will need to modify the VLAN settings on each individual port. How can I do this?
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Mar 14, 2013
I need a switch to configure a static ARP entry for a MS NLB multicast.
Could answer me if I can do with the SRW2024-K9-BR?
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Aug 23, 2009
Aug 24 11:32:16.275 AEST: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan21, changed state to down
Aug 24 11:32:36.827 AEST: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan21, changed state to up
Aug 24 11:35:23.854 AEST: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1/2, changed state to down
Aug 24 11:35:24.854 AEST: %LINK-3-UPDOWN: Interface FastEthernet0/1/2, changed state to downesw_mrvl_vlan_port_remove : Unable to find entry for VLAN(1) dbnum(1)
esw_mrvl_vlan_port_remove : Unable to find entry for VLAN(1) dbnum(1)(code)
When the above problem happens, as work-around, we delete VLAN.DAT file on the Compact Flash of this 2811 router and recopy the VLAN>DAT file back to teh Compact Flash.
Then it runs for a few weeks and the same problem happened.
Then we put a new Compact Flash and recopied VLAN.DAT to new CF and it ran for 3 weeks and same problem started again.
Could be 2811 router motherboard? This customer has thousands of these 2811 routers in identical setups and this is the only router that is having this problem.
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Mar 17, 2013
If a router receives EIGRP (AD90) routes, and is configured to redistribute thoes routes into BGP(AD20), why does the RIB show only the incoming EIGRP routes and not the redistributed bgp routes? Are redistributed routes considered for RIB entry in the router that is doing the redistribution
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Mar 7, 2012
We have a Cisco 1841 router that requires 2 levels of access, at the moment we have network admins logging in with a single username via SSH and with privilege 15 but we also need our helpdesk to login to run certain commands but not chaneg anything
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Oct 7, 2012
I've never had a router's CPU suddenly hit 99% and just stay like it for hours even after a reboot. This router really does nothing with regards to CPU, I'm looking at it's CPU history (via SolarWinds Orion NPM software that we use) and it is arounf 1-3% all the time for the past 2 years.
I did a show debugigng and it seems no debugging is running
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Jun 5, 2012
We currently have a Cisco 1841 router with version 12.4(1c) of IOS using image c1841-ipbase-mz.124-1c.bin. Our goal is to make it so our router can fully support IPv6. The current IOS version cannot. I've seen a site that seems to indicate 12.4T does support with IP Base image but recently had Cisco tell me with the latest IOS release 15.1.4.M4 that I have to use either the "Advanced Enterprise Services" or "Advanced IP Services" image. Did Cisco just remove IPv6 from IPBase in later IOS releases?
Also I've seen conflicting specs on the max amount of Flash and DRAM the router can support. The following link shows that 384MB is the max for DRAM and 128MB max for flash. We're looking to upgrade ours from 128MB and 32MB respectively but as mentioned I've seen it where higher amounts are supported. In fact we bought a backup 1841 to have and it has a 256MB Flash card in it.URL
Last but not least. Where can I find a straightforward documention of this situation where we may have to upgrade our Flash and DRAM and then upgrading the IOS?
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Nov 12, 2012
We have two Cisco 3560E layer 3 switches at the core of our network. The switches are configured as an HSRP pair and the clients on our network point to the HSRP address as their default gateway. So if CORE-A dies, then CORE-B will pick up the address and the default route for the clients will continue to be available.We also need to specify a few static routes on the core switch to allow us to get to specific networks. Is there a way to do this so that the routes failover in the same way that the default gateway does?
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Dec 5, 2012
I started using RIPv2 on Packet Tracer. I got two subnets to connect with two routers. After I completed that, I decided to add a third router. How to setup the Routing Table for atleast R3 ?
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Oct 2, 2012
I am using Cisco 2911 & IOS version is 15.1. My problem is that after some days (e.g. 15-20 days), the routing table suddenly stops updating & then I have to enter the default route again to make it up. I am using Track 1 to track default route here. After primary link goes down, the Track is also going down but after coming the primary link up, the track is not coming up. So, I have to add the default route again to make it up.
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May 22, 2013
I am attempting to filter a specific host(s) from my OSPF routiing table on a ASA 5550 (ABR) using LSA prefix lists. However, when I look at the other routers in that area, I notice that ALL LSA type-3's are being removed (10 hosts are now missing from the routing table). I have verified the filter is working on the ABR, but I can't figure why ALL hosts/routes that were coming into the area are now being filtered instead of the specific one that I want to filter out.
Here is the config on the ABR:
prefix-list pdm_pl_000 seq 10 permit 206.253.180.137/32
!
!
router ospf 1
network 10.0.0.0 255.255.255.0 area 0
network 10.150.10.0 255.255.255.0 area 10
network 10.150.252.0 255.255.255.224 area 10
[code]....
The 206.253.180.137 host is actually coming from Area '3'. Am I doing something that is removing all type-3 LSA's?
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Nov 18, 2012
I have got a l2 link of 512 kbps from two different ISP. I want to aggegrate the bandwidth of this connection so that I can feel like having 1 mbps connection. I am not actually talking about load balancing, but bandwidth/link aggegration. Can we have the solution of failover with different vlan from different isp ? Can we be able to make the link as a single link.
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Mar 16, 2013
establishing a Static NAT on an 1841 router.
I'm at a FOX affiliate TV station, and in order to connect our EAS Device to the internet & Fox Splicer, I need to setup a Statio NAT, so we picked up an 1841 on eBay.
I've done a little configuration in HyperTerminal.
I've done these ip addresses:
FE0/0 10.1.10.13 this is the subnet our EAS device is on
FE0/1 10.110.81.174 this is the subnet of the Fox Splicer.
I need to have NAT translate 10.1.10.11 to 10.110.81.170 and I also need to set a route for 10.110.81.0/24 pointing to 10.110.81.161
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Sep 16, 2012
Hava cisco router 1841 forgot user name and password and need to reset it to its factory setting
tried boot while holding ctrl and break get into rommon1>
rommon1>confreg 0*2142
rommon1>reset
still shows rommon 3>
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Jan 6, 2012
I have the following devices for our IT Test LAB
1. Cisco 1841 with 2 Fast Ethernet interfaces fa0/0 & fa0/1
2. Cisco 2960-S
3. Speedstream 6200 DSL Modem ( PPOE Connection with Static IP address)
I want to connect to the internet using the current DSL connection we currently have .
LAPTOP --> SWITCH 2960 --> ROUTER 1841 ---> DSL Modem ---> ISP
Troubleshooting 1: Currently from the LAPTOP i am able to ping
1. Switch 2960 Vlan interfaces
2. Router 1841 fa0/0 & fa0/1
BUT can not Ping the DSL Modem LAN interface IP 192.168.2.1 and can not get out to the INTERNET
Troubleshooting 2:currently from the Switch 2960 i can ping
1. All the Vlan interfaces on the Switch 2960
2. Router 1841 fa0/0 & fa0/1 interfaces
3. Laptop A & B
But can NOT ping the DSL modem LAN interface IP 192.168.2.1 and can not get out to the internet
Troubleshooting 3:Currently from the Cisco 1841 router i can ping
1. All the Vlan interfaces on the Switch 2960
2. Router 1841 fa0/0 & fa0/1
3. Laptop A & Laptop B
4. Can Get out to the internet. I am able to ping any internet destinations without any problem
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May 12, 2012
Any simple way of opening ports on a 1841 router.I have a working config for internet traffic. I am looking to boot up my Windows Server and Run IIS.
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Nov 6, 2012
due to upcoming changes to our network I'd like to be able to pass vlans across the FE ports of a Cisco 1841 router.1 port would go to a managed switch and then to local devices on different VLANs.the 2nd port would go upstream to a Cisco 3825 at a different location which would then connect to the internet.due to monitoring behind the Cisco3825 we would like all NAT to occur on the 3825.
what I would like to happen is this example device connected to port 7 on managed switch gets an IP (10.0.7.10) from the Cisco 1841 in VLAN 7 (10.0.7.0/24).traffic from that device goes to the switch, then in f0/1 on the 1841 and out f0/0 still with the same IP info, no NAT occuring.traffic is received on the 3825 port 0/1 and then NAT occurs and out port 0/0 to the internet.
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May 12, 2013
I have 10Mbps internet speed connected to ciusco router 1841 that has 2 internal NICs. One NIC has a full 10Mbps download speed and the 2nd NIC is currently limited to 1Mbps download speed. I want to change the download speed of the 2nd NIC to 4Mbps? How do I do this on a cisco 1841 Router?
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May 26, 2013
We have a setup of a firewall in between my Cisco 1841 router and Switch.
Cisco Router --> Meraki Firewall--> Switch
Client VPN is configured on the Meraki Firewall but then for the outside users to client vpn in to the network, I have to port forward or open the ports 500 and 4500 to the IP address of the Meraki Firewall 192.168.1.90. [code]
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