21 votes
Accepted

ASICs vs x86 general-purpose routing/switching

Is it correct in assuming that ASICs for router or switch interfaces will outperform the use of an x86 CPU for all packet processing which will greatly suffer from CPU interrupts? It's hard to say ...
user avatar
12 votes
Accepted

Should I disable STP on my access ports?

You really, really do not want to disable STP where you connect switches to other switches. That is the entire purpose of STP. If you disable STP, and there is a problem, it will really be too late ...
user avatar
  • 93.4k
11 votes
Accepted

Meaning of the ip default-gateway L2 switch

tl;dr The switch management cannot send anything to a different layer-3 network without a default gateway. Telnet is a bidirectional protocol, and the switch, without the default gateway, would be ...
user avatar
  • 93.4k
9 votes
Accepted

Can Cisco Catalyst switch get IP from DHCP server?

You can specify an interface to receive an address from DHCP like this. configure terminal interface (int-name-num) ip address dhcp This guide gives way more detail into DHCP features - Cisco DHCP ...
user avatar
  • 6,440
9 votes
Accepted

Locked myself out of my Cisco switch

If you didn't save the configuration, you could just restart the switch, but you will need physical access to the switch. You may be able to get someone at the site to restart the switch for you. ...
user avatar
  • 93.4k
8 votes
Accepted

When and where to use Spanning-Tree (Portfast)

Spanning tree only runs between switches, never to standard end hosts. Bear in mind that, under normal circumstances, a port supporting spanning tree will (when it first comes up) run through a ...
user avatar
  • 6,028
8 votes
Accepted

2960X Management VLAN

You can disregard the dedicated management interface and simply assign an IP address to the VLAN 500 interface on the switch and use this IP for management purpose, with appropriate access lists. FE0 ...
user avatar
  • 18.4k
8 votes
Accepted

Switching interface VLAN ID Mid-Production

I was wondering if there was a way to switch out the VLAN ID from VLAN1 to VLAN10 without impacting the connectivity of the end users? No. First, you must remove the addressing from VLAN 1 before ...
user avatar
  • 93.4k
7 votes
Accepted

cisco 2960G won't boot and no console output

Open a TAC case as these may be affected by this Field Notice. This revolves around a known memory issue by parts from a particular supplier that have a high failure rate. These parts have been ...
user avatar
  • 26.7k
7 votes

Overlapping IP addresses in CISCO 3650

Your subnet mask is 255.255.0.0 (also written as /16). That means the first 16 bits of the IP address define the network, and the last 16 bits are the host address. With that mask, there are 65534 ...
user avatar
  • 62.4k
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. ...
user avatar
7 votes

How to Change the Date on Cisco Catalyst 3750x Switch

The order of operations is important because setting the time first will result in the time being incorrect after issuing the zone commands, so what you need to do is: First, you set the regular time ...
user avatar
  • 4,481
7 votes

How do I know the switch is layer 2 or layer 3?

In addition to @Zac67 answer, in the Catalyst product line, layer 3 capabilities are often unlocked by licenses. So a given switch can be layer 3 capable but, depending on the installed license, may ...
user avatar
  • 18.4k
6 votes
Accepted

Cisco 2960-X Discover SFP Modules Without Rebooting

Maybe these bugs are affecting you: CSCuj74167 (Gigabyte link from WS-C2960X-48FPD-L not coming up when using GLC-SX-MM) applies to you. Fixed in software release 15.0(2)EX4. CSCul88801 (1G or 10G in ...
user avatar
  • 655
6 votes

cisco 2960G won't boot and no console output

This is not a fix but a workaround to get your switch boot up. It did worked on my 2960G. WS-2960G has a reset switch SW2 that hasn't been soldered (see picture). By shorting those two soldering ...
user avatar
  • 61
6 votes
Accepted

max number of supported MAC addresses in Catalyst series switch

Yes, but this might be platform dependent. For example, on Cisco 4900M: 4900M#show mac address-table count MAC Entries for all vlans: Dynamic Unicast Address Count: 8507 Static ...
user avatar
  • 628
6 votes

Cabling standard for Layer-3 switch

I want to know the appropriate cable type between: Layer-2 and Layer-3 switch Layer-3 switch and router Is it cross-over or straight through? You need to make the distinction ...
user avatar
  • 1,616
6 votes
Accepted

Will a Wi-Fi Access point affect maximum addresses configured via port-security

That depends on how the access point is configured. If it's configured as a router you'll only see one address of the access point itself, but if it's configured as a bridge between the wireless and ...
user avatar
  • 15.6k
6 votes
Accepted

Basic Catalyst 3560 Egress Shaping

And now the real question: To shape all unclassified egress traffic to fit into 50 Mbps, can I just enter srr-queue bandwidth shape 0 2 0 0 on the interface in question and be done? It ...
user avatar
  • 1,125
6 votes

What should a device do with an Ethernet frame larger than its MTU?

The ethernet standard (IEEE 802.3) calls the large frames damaged because the bits where the FCS is supposed to be don't match the CRC of the bits coming before them. What you see the Cisco switch do ...
user avatar
  • 93.4k
6 votes
Accepted

Port channel to two different switches

I understand that this is an incorrect configuration, but what was blocking traffic to the new switch? Is this part of the port channel or spanning tree or something else? Nothing was actually "...
user avatar
  • 26.7k
6 votes

Factory Reset Cisco 3560: Stuck in loop

Sounds like a nice job of a botched content ot the boot variable - possibly the config file variable. The switch: prompt you see there is called the ROMMON prompt. ROMMON is a bit like the BIOS of a ...
user avatar
6 votes
Accepted

Cisco 3750G - SSH Diffie Hellman Group 1 SHA1 Error

Your SSH client is saying "we can't agree on the cipher: server wants X but I'm configured not to speak X". This is a completely general SSH problem, not specifically related to this model of switch, ...
user avatar
  • 15.9k
6 votes
Accepted

QoS policy definition - Cisco guidelines vs reality

If you are using eight classes, then you are probably overthinking it. You want most traffic to be in the default class, protect real-time traffic with a priority class and policing, make sure that ...
user avatar
  • 93.4k
6 votes
Accepted

cisco switchport trunk native vlan

The problem is not the traffic from the server to the switch, but the return traffic, from the switch to the server. Since the VLAN is native, the switch will sent the traffic for this VLAN untagged, ...
user avatar
  • 18.4k
6 votes
Accepted

PortFast For Some Networks But Not Others

We don't know the configuration of your servers and PCs - which is off topic here. Portfast allows the switch ports to transition their spanning-tree mode to forwarding immediately. Without Portfast, ...
user avatar
  • 62.4k
5 votes

802.1x on Access VLAN only, not on Voice VLAN

802.1x is port based. So, in simplest form, the port is either authorized or not; once authorized -- MAC limits aside -- traffic from anything will be allowed. Modern 802.1x systems are much smarter ("...
user avatar
  • 29.6k
5 votes
Accepted

Rolling Stack Upgrade on a Catalyst 3850

Nope, sorry. That's why I prefer daisy-chaining to stacking, even though I lose out on some bandwidth and a couple of ports. There are some helpful hints on the upgrade here, though: https://...
user avatar
  • 1,783
5 votes
Accepted

KEMP load balancers using UCARP (VRRP) - multicast MAC address not being picked up

I was able to resolve the issue. On the Kemp (with HA pair) you have the option of using a "Virtual MAC Address". If this box isn't checked, then the MAC of a load balancer VIP is that of the physical ...
user avatar

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