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.
...
- 30k
6
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 ...
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 ...
- 16.4k
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.
...
- 165
3
votes
What can I infer about a network connection using a cable tester (if anything)
This type of cable tester is intended for bare cables only. Connecting it to a live network can damage the network component on the other side or (more likely) the tester itself, esp. on a PoE link.
...
- 88.1k
3
votes
Accepted
What can I infer about a network connection using a cable tester (if anything)
According to the instructions for the NS-468, it is designed and engineered to use the master unit at one end of the cable and the remote unit at the other end of the cable.
Based on the instructions,...
- 27.4k
3
votes
Accepted
Adding encrypted password on Cisco 3560-CG switch
You are receiving the error because the "password" you are entering is not a proper MD5 hash. Check to verify that you are trying to enter a complete MD5 hash and that it is not another type of hash. ...
- 1,241
3
votes
How to verify Voice QoS dscp and IP predecence traffic session?
To see actual traffic for each class:
show policy-map interface gi0/0
In order to see actual traffic passing through the interface you'll need some kind of network sniffer with combination of port ...
- 1,133
3
votes
DLink switch loses configuration on power off!
This has just happened to me with my Dlink DGS 3120-24SI.
Apparently you need to go to the web gui then select Save ... Save Configuration / Log.
Change Type to All, then Apply.
This saves everything ...
- 31
3
votes
Cisco Router IOS update
Don't delete the IOS from the flash>
PLease share the output
# show boot -- check the NEW IOS is in the next reboot if not do below command.
conf t
boot system flash:IOS image name.bin
Save the ...
3
votes
How can you determine the result of a load-balancing hashing algorithm (such as ECMP/LAG) for troubleshooting?
There are some things to test in certain circumstances, but the basic idea is that PAgP or LACP aggregations are between two directly-connected devices, and anything sent from one device to the other ...
- 101k
3
votes
Do wiremap testers detect split pairs
Most do, but not necessarily all of them - some just test for DC continuity and shorts. While the term is widely understood among professionals, there may be vendors trying to fool you. After all, ...
- 88.1k
3
votes
Accepted
Wireshark filter for specific SYN packet which never received a SYN/ACK
According to https://osqa-ask.wireshark.org/questions/60995/how-do-i-filter-tcp-connection-with-syn-and-syn-ack-without-ack-response/ you can do this by applying a filter (tcp.flags==0x12) and not tcp....
- 154
2
votes
Interpreting TTL in ping results
TTL values are determined by the remote machine. For example, if you ping a Linux machine, its originating TTL value is 64. Depending on how many routers it crosses to get back to you, the TTL is ...
- 21
2
votes
Time exceeded ICMP in Serial Interface [Cisco Router 2811]
Serial x is up, line protocol is up (looped)
A loop exists in the circuit. The sequence number in the keepalive
packet changes to a random number when a loop is initially detected.
If the ...
- 969
2
votes
Accepted
Time exceeded ICMP in Serial Interface [Cisco Router 2811]
Serial0/0/0 is up, line protocol is up (looped)
You interface is looped and hence when you ping the IP 210.220.61.1 on the other end you are stuck in the loop and hence TTL(hop count) gets expired, ...
- 343
2
votes
Accepted
Juniper EX4200 firewall filter applied to trunk port not matching specific VLAN
This appears to be a defect - I just recreated a similar environment on an EX42000-VC running 15.1R3.6.
family ethernet-switching {
filter LIMIT-VLANS {
term VID10 {
from {
...
- 9,565
2
votes
Intermittent periods of high packet loss, one hop beyond router
Shielded cable does not perform as well as unshielded cable if it is not properly grounded, and the shield will actually create problems by reflecting internal signals back into the cable. Unshielded ...
- 101k
2
votes
Accepted
arp or proxy-arp causing high cpu
Fault is now resolved. We didn't have a topology beyond our ASR901.
We know in normal circumstances the ARP table and the mac-address table have no relation to each other, however that is not the ...
- 480
2
votes
DLink switch loses configuration on power off!
Previous answer given by patch67:
go to web gui, Save Configuration / Log. Change Type to All, then Apply.
works perfectly for my device: dgs-3120-48tc
- 21
2
votes
Accepted
Help me understand this netstat report
Doubleclick is an ad service for websites. What you are seeing is someone who went to a web site that had doubleclick ads. Web browsers will open multiple connections when viewing a web site in order ...
- 101k
2
votes
Accepted
Can't connect to FTP
open 192.168.1.1 log in to your modem and go to advanced-->nat--->alg--> turn on FTP and save and you're done
- 46
2
votes
how to capture only SMTP using latest Wireshark 2.2.6 or later
Filtering while capturing data in Wireshark is documented here: https://wiki.wireshark.org/CaptureFilters
An example of such for SMTP is: tcp port smtp
Filtering already captured data is here:
https:...
- 642
2
votes
How to Troubleshoot Network Latency Step by Step
Very likely the WAN connection is the major problem. There's little you can do except provide a local server or change the ISP. Additionally, the possibly weak WAN link may be congested and may need ...
- 88.1k
2
votes
Accepted
How do I find out which NAT is getting hit?
You can find that out by using the packet-tracer feature. To use it from the CLI, you would issue the command:
packet-tracer input <name of your source interface > <protocol> <source ...
- 4,690
2
votes
Cisco 2821 hangs with "No memory"
Short answer is this: You do not need to enable any debugs to have Traceback messages sent to syslog, provided the router can send those messages upon crashing (which does happen sometimes, thanks to ...
- 1,033
2
votes
Steps on troubleshooting a network
If the link is physically down, the steps are very easy.
Check port configurations (shutdown, manual speed/duplex selection).
Check port compatibility (twisted-pair ports are not all downwards ...
- 88.1k
2
votes
How can you determine the result of a load-balancing hashing algorithm (such as ECMP/LAG) for troubleshooting?
I've been using this command on NX-OS, on a set of N3K-3164Q:
switch# show routing hash <srcIP> <dstIP> ip-proto <protocolNumber> <srcPort> <dstPort> vrf <vrfName>
...
- 8,876
Only top scored, non community-wiki answers of a minimum length are eligible