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23 votes
Accepted

Interpreting TTL in ping results

So needless to say, nobody on the planet knows how many nodes there are between here and there. I know how many nodes. There are exactly 16. The reason you get different responses is because ...
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  • 62.1k
16 votes
Accepted

Edit Cisco IOS ACL without hanging the router

The reason your router hangs is because you're editing the ACL through the same interface that it's applied to. Usually what happens is you wind up blocking yourself accidentally. Note that I make a ...
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12 votes

How to verify that a UDP port is open?

UDP is obviously a send-and-forget protocol. For example, during an NMap UDP scan, the only way to definitively prove that a UDP port is open is if you receive a response from that port. Keep in mind ...
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  • 435
12 votes

How to verify that a UDP port is open?

This is a quick recipe: 1) Start a packet sniffer: sudo tcpdump -n -i eth2 icmp & [1] 1409 $ tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth2, link-...
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  • 1,616
10 votes
Accepted

What is an acceptable spell of total packet loss for public Internet traffic?

The issue: Customers can experience total packet loss for 10s, 30s and more. This brings the TCP connection delivering the prices to a halt, thus rendering the website useless. All connectivity from ...
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8 votes
Accepted

Cisco + FreeRADIUS: Exec 15 level privilege mode

It seems that this line is missing from the c2600... aaa authorization exec default group radius local Exec authorization is what gives a login session the ability to pay attention to priv ...
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7 votes
Accepted

Fix our Cisco switch overwhelmed by console logging

I have a setup with dual redundant Cisco catalyst 4506-E using the WS-X45-SUP8L-E supervisor engine and two 48-port switches below it. My task is to access and modify the switch configuration. ...
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6 votes

MTR packet Loss at intermediate hop

However, when we run the same WinMTR tool to our gateway, we receive a 0% packet loss on the gateway, but as of last test a 9% packet loss on the router... [snip] ... I'm not entirely sure how to ...
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6 votes
Accepted

Unpredictable Juniper SNMPv3 Access Error

This issue is a result of the engine-id changing. If you run into this syslog message, that is the exact definition of the problem. Nov 6 09:44:35 MHN00416AN01 snmpd[1260]: SNMPD_ENGINE_ID_CHANGED:...
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  • 5,449
5 votes

What is an acceptable spell of total packet loss for public Internet traffic?

Total Packet loss for 10-30 seconds is surely caused by other factors than lost packets somewhere on Internet. A lost tcp packet would normally generate a retransmit within ~10-100ms. Congested links ...
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  • 141
5 votes
Accepted

Strange drop-outs in Cisco 7200 LNS lab

Testing that kind of features using GNS3 is simply waste of time. You're emulating at run-time complex software, and on top of that, you're adding complex features. There's no sense in 'trying' 7200 ...
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5 votes
Accepted

CPU Impact of "debug ip packet" on Cisco Switches

The platforms you mention are all hardware forwarding devices. What debug ip packet does is to show packets going to / from the switch's CPU (either punted, locally-sourced, or control-plane). You ...
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  • 7,448
5 votes

How to verify that a UDP port is open?

"nc -uvz ip port" isn't somehow accurate, you probably should use "nmap -sU -p port ip", if the result shows "open" then the udp port probably is open, if it shows "open|filtered" then probably it is ...
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5 votes

Cisco 1800 series: sys-2-chunkexpanfail: error every time

If you are on release 12.4(15)T12 | 12.4(24)T2 then this could be related to a Cisco bug CSCtg26917 with more details on it here Symptom: Chunk manager consume almost all memory. We found the ...
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  • 1,966
5 votes
Accepted

PAT not translating at all

Looks like the NAT access-list 1 is too tight. host 10.0.0.0 will only match the single host with address 10.0.0.0, and you have no such host. You almost certainly wanted this: access-list 1 ...
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  • 15.9k
4 votes
Accepted

Cisco ISE backup shows as success but no data was written to backup server

The problem ended up being a permission issue on the backup server. This didn't seem to be a problem since ISE was able to read the backup folder. I also thought this was an issue on ISE's side since ...
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  • 754
4 votes
Accepted

Multiple error types Cisco 861 router

@PHLiGHT, hello there! your cisco 861, imho, has overloaded by ingress traffic. Lets look on your cisco iface counters: 5 minute output rate 198000 bits/sec, 56 packets/sec 157099395 packets ...
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  • 926
4 votes
Accepted

Problem with IP phones after ISP failover change

From your description of the issue, this could be related to the UDP connections not being torn down from the Backup interface once the Main interface becomes available. You can use the following ...
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4 votes
Accepted

HW State: DEAD - Cisco 3925

Yes, the VPN module is a linecard that's plugged into the router and can be replaced. A 'DEAD' hardware state simply means the router has lost communication with the ISM. This does not actually ...
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  • 599
4 votes
Accepted

Juniper EX2200 can't boot

All the SCSI errors indicate a broken disk, or a disk about to break. Request an RMA at JTAC if you have support. If not, you may be able to find some hints on the internet on how to replace the disk, ...
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  • 15.6k
4 votes

How do I pinpoint bandwidth consumers on my Fortigate?

This sounds like a case study for sFlow. The best way for you to figure out what's going wrong is to figure out who's talking to who - and how much. Just spin up your favorite sFlow analyzer and ...
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  • 5,449
4 votes

How to find the end-device causing high cpu usage in a Cisco switch?

What is driving CPU usage in a Cisco switch is probably not a single end-device. Cisco switches can normally handle a full switching load without driving the CPU utilization unusually high. This is ...
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  • 93k
4 votes
Accepted

Is it possible to tell if a firewall is present on my network path?

Traffic can be routed between VLANs by a router, there is no requirement for a firewall (which ultimately is really a router with some filtering features, anyway). There is no way to say for sure ...
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4 votes
Accepted

Steps on troubleshooting a network

Handy way to start troubleshooting is from Physical Layer following OSI Layer Model Check physical port/cable (as mentioned by @Zac67 also) Check port negotiation & Duplex, speed on both ends. ...
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3 votes

Troubleshooting "TCP Zero Window" Issues

Well. Since you've captured packets that show that your Trading Server is sending the TCP ACK's with a window size of 0, you at least know the problem is definitely on your side. Which is actually a ...
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  • 13.9k
3 votes
Accepted

Troubleshooting low Metro Ethernet TCP throughput

While discussing this problem was very interesting, the ISP has in the meantime started exchanging the DSL modems on the different sites by another brand. Some packet fragmentation issue they say. And ...
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  • 1,173
3 votes
Accepted

TCP Reset-I on Cisco ASA 5512x version 9.1

If you only have a single subnet behind the firewall, I would try something like this. object network inside-net subnet 192.168.1.0 255.255.255.0 nat(inside,outside) dynamic interface dns You would ...
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3 votes
Accepted

Cisco 3560X Switch MAC reported with same IP as other equipment

Hope this helps as I had the same issue and this corrected the problem. 568750 - False Duplicate IP detection on Logix Ethernet modules when used with Cisco switches Access Level: Everyone Date ...
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3 votes

Split Horizon will not disable on interface

Try adding this command to your tunnel interface. Your spokes are receiving routes with the next-hop as the hub router without it. no ip next-hop-self eigrp 1601
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  • 549

Only top scored, non community-wiki answers of a minimum length are eligible