The Stack Overflow podcast is back! Listen to an interview with our new CEO.
35

The counter is increasing because your frames are being corrupted. CRC is a polynomial function on the frame which returns a 4B number in Ethernet. It will catch all single bit errors and a good percentage of double bit errors. It is thus meant to ensure that the frame was not corrupted in transit. If your CRC error counter is increasing it means that when ...


34

The answer depends on whether the switch is a Layer 2 or a Layer 3 switch. That is to say, is the switch only switching and relaying traffic on to a different device for routing, or, is it doing the routing decisions itself via SVIs (switched virtual interfaces). On a layer 3 switch, the port can be found by using a few simple commands on the device. ...


22

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 different operating systems use different starting values for TTL. Some devices use 255, while others use 63. So, one of the devices you are pinging sends the ...


20

Referencing our Stack Exchange chat... Short story, you need to control the speed mismatches on both sides of your metro Ethernet links... I redrew your diagram for the sake of clarity... Note 1 The DC (shown in green) transitions from 10GE to 100M very quickly... this is a 100-fold speed transition, and you commonly need to implement some form of qos (...


16

RSSI is a Radio-Frequency (RF) term and stands for Received Signal Strength Indicator. It is a measure of the power level that a RF device, such as WiFi or 3G client, is receiving from the radio infrastructure at a given location and time. For instance, the power level a laptop is detecting from a nearby AP. Usually, the higher the RSSI the better the ...


16

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 suggestion for reorganizing your ACLs at the bottom of this answer, although most people will be interested in this first section (the easiest way to change ...


15

MTR uses ICMP, which is often rate limited on the internet due to how it can be misused to created problems (high CPU, wasted bandwidth, DoS, etc). When you see output like this, generally this is a sign that rate limiting for ICMP is in place. With a quick web search I found this documentation regarding using MTR. While it is not official it looks decent ...


14

As @YLearn already wrote ICMP ratelimiting on the router with packetloss might well be the cause, because replying to ICMP requests is done in CPU while forwarding of packets is usually done in the ASICs. So this does not need to be a problem at all. A very good guide on interpreting traceroute (and MTR) output was written by Richard Steenbergen a few years ...


14

The closer the figure is to zero, the better. So in the figures you've given above, -75 is better than -100. In my experience -75 provide a reasonable service. -85 provides an OK service. -100 provides a barely usable service. -110 provides no service at all. This figure represents your signal strength to the cellular tower. The closer you are to a tower, ...


13

Firstly, you need to get the MAC address, so get into a machine on the same VLAN and look at its neighbour table - Windows is netsh int ipv4 show neigh, Linux: ip nei Cisco: show ip arp x.x.x.x. Once you have that... If this is a discovery job on a layer 2 switch, do show mac address-table | i 0011.2233.4455 - replacing the mac address bytes as appropriate. ...


13

You could monitor the traffic on the router, Cisco IOS 12.4(20)T and later, there is a packet capture feature, with filtering on interface name and direction and ACL. set up an access list for matching the traffic create a capture buffer monitor capture buffer holdpackets filter access-list <number> define a capture point monitor capture point ... ...


10

The ASA5550 requires the SSM-4GE-INC module to be plugged into the chassis1 when it is booted; if it is not, then you get assertion "_vf_mode_init" failed: file "vf_api.c", line 99 printed to the console. I discovered this2 after opening a case with TAC (who did not catch this problem), RMA'ing the original chassis, and then unplugging the SSM-4GE-INC ...


10

Since you are temporarily able to ping the server, VPN and ACLs should be fine. I recommend to verify: A local firewall on the server could block the ICMP requests. The fact that it responds at startup, but stops later, leads to this assumption. There may be an IP conflict, i.e. another device in the network with the same IP. That cause is possible since ...


10

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 that many services may not reply to arbitrary data and require protocol or application-specific requets in order to warrant a response. Certain ICMP codes can ...


9

The difference between aggregate labels and normal labels is such that normal labels directly point to L2 rewrite details (an interface and L2 address). This means a normal label will be label switched by the egress PE node directly out, without doing an IP lookup. Adversely, aggregate labels can potentially represent many different egress options, so L2 ...


9

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 the data center to the peering points have been sized correctly, and have capacity to spare. It has been asserted that this is commonplace in public ...


8

This took less than 2 seconds on Google: HP networking portal HP ProCurve 5400zl Switch Series - High CPU Utilization (99-100%) after Startup Issue Right after the switch is started, high (99-100%) CPU utilization is observed. Solution When the switch boots, one of the initialization tasks is creation of encryption keys. Having the keys ...


8

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 information from the RADIUS server.


7

The latter half of your question seems to indicate you're looking for latency figures that take into account the process of forming application-layer data, in which case "ping" will not help much considering there's not much data to be formed in a ping packet. Network folks usually rely on ping because it's a relatively light and reliable way to produce a ...


7

Regardless of whether your switch is performing frame forwarding (layer 2) or packet routing (layer 3), the following should work if the switch has a management IP address in the same subnet as the host you want to find: At the switch, ping the IP address you want to find. If the address is on the same subnet as the switch's management address, an ARP ...


7

OK, after looking at your configuration, you are missing one statement: route outside 0.0.0.0 0.0.0.0 125.x.x.9 This tells the firewall to forward all Internet traffic to the ISP's router at 125.x.x.9


7

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-type EN10MB (Ethernet), capture size 262144 bytes 2) Send an UDP packet: $ echo reply-me | nc -u 1.0.0.2 1000 3) If you receive 'ICMP port unreachable', that ...


7

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. Access shall be accomplished locally only, through console port using serial cable and user/pass combo. The notion that "thou shalt not use ssh / telnet /...


6

It can't be PC ethernet card, as DES-1024D is not 'cut-through', that means, if PC sent broken frame, DES-1024D dropped it and did not forward it. You've already done good debugging by moving the wire to another switch, this allows us in high degree of confidence to exclude 3COM as culprit for the errors. Options that are left is room 3 D-Link or wiring ...


6

Make sure that you have created the repository using the following commands from the Command Guide. (Remote sftp repository for example below, but you could use tftp, ftp, etc): ncs/admin# configure terminal ncs/admin(config)# repository myrepository ncs/admin(config-Repository)# url sftp://example.test.com/repository/system1 ncs/admin(config-Repository)# ...


6

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 process this information... You've misunderstood how WinMTR should be used; this is a common problem. The first line you should look at in any mtr output is ...


6

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: Warning: Local engine ID has changed. Passwords for all the users under [edit snmp v3 usm local-engine] need to be reconfigured. Unfortunately, I have ...


5

On the ISR G1/G2 routers you can use packet capture feature, where you use ACL to match the traffic and store it into memory during capture, then dump to .pcap compatible format if you need it offline: https://supportforums.cisco.com/docs/DOC-5799 On the Catalyst 4500 with newer Supervisors you can actually run wireshark.


5

Do you have the option of using IP SLA between two routers at each point? I'm not sure about your topology at the remote end so not sure if you have a server on the other side or if that server connects to a router which could in theory run IP SLA


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