18 votes
Accepted

What does logging synchronous command do?

"logging synchronous" prevents every logging output from immediately interrupting your console session. See command documentation: "This keeps unsolicited messages and debug output from being ...
user avatar
  • 1,626
13 votes
Accepted

What does no shutdown command do? Cisco

In the simplest sense, shutdown turns the interface off. no shutdown turns the interface on (enables it). You can configure an interface in either case. Using the shutdown command is one of the ...
user avatar
  • 63k
13 votes

Why does the Cisco show run command not show the full version, while the show version command does?

Is there any reason why Cisco show run does not show the full version which is 16.3.7 in this example? For the simple reason that the only the major and minor versions are necessary for a complete ...
user avatar
  • 26.8k
12 votes
Accepted

How to Disable telnet on Cisco switch totaly?

If you actually configured line vty 04 Then you have something like: line vty 0 3 transport input telnet ssh line vty 4 transport input ssh This is because you configured only the fifth VTY ...
user avatar
  • 18.4k
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
  • 94.1k
11 votes
Accepted

Why does the CISCO's command 'enable secret <password>' produce different hash from MD5?

Cisco devices add a salt to the passwords before hashing so they can't be cracked with dictionary attacks (such as rainbow tables). The salt is partially made up of the device ID, if I recall. MD5 is ...
user avatar
  • 4,661
10 votes

How can I reset a VPN tunnel on a Cisco ASA?

I just came across a new way that I was never aware of before and offers the same information you find in the ASDM interface, including the feature to logoff a vpn session. Issue this for example to ...
user avatar
  • 201
10 votes

Why does the CISCO's command 'enable secret <password>' produce different hash from MD5?

$1$ marks the MD5-crypt password hash also commonly used in past years for user passwords in Linux systems. In that function, it's now been pretty much superseded by the similar SHA256-crypt and ...
user avatar
  • 236
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
  • 94.1k
9 votes
Accepted

Duplex Mismatch Detection

Packet Tracer is a simulator aimed at CCNA level courses. It doesn't accurately simulate real devices but only a subset of their functions. (and still those simulations aren't perfect). I would not ...
user avatar
  • 18.4k
8 votes
Accepted

"transport input" for AUX port in Cisco routers

On physical layer AUX port works on asynchronous serial RS-232 protocol. However, one can specify various application layer protocols like telnet or SSH as allowed input protocols under AUX line ...
user avatar
8 votes
Accepted

Cisco IOS versions vs Cisco ASA versions?

Cisco has a whole bunch of different operating systems for a variety of products: IOS runs on most Cisco routers and switches. IOS XE is a more modern, modular version of IOS. IOS XR runs on high-end ...
user avatar
  • 1,909
8 votes

What is the difference between "ip domain name" and "ip domain-name"?

The two forms are equivalent. "domain-name" is the older form, and newer versions seem to prefer "domain name". Maybe at some point Cisco realized that removing the hyphen allowed them to extend the "...
user avatar
  • 2,396
8 votes
Accepted

What is the difference between "ip domain name" and "ip domain-name"?

They are the same. Cisco IOS also supports the command ip domain name starting from its 12.2 Software release. You can check it here: IOS: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipaddr/...
user avatar
  • 3,744
8 votes
Accepted

set cli complete-on-space Cisco equivalent

The Cisco command completion uses the <TAB> key (one of the Juniper options). Cisco commands also do not even need to be complete to work; they only need to be complete enough to be unambiguous....
user avatar
  • 94.1k
7 votes
Accepted

When switchport port-security violation protect( or restrict) is configured , how many times can the security policy be breached?

Yes, the restrict and protect modes can be violated any number of times without shutting down the port since they are not designed to do that; they will drop packets with unknown source addresses: ...
user avatar
  • 94.1k
7 votes

What do these three options in a Cisco Router NAT configuration mean?

Think about this very carefully. Inside source means that you want to translate the source address from traffic originating inside your network. This is the typical "home networking" arrangement ...
user avatar
  • 94.1k
7 votes
Accepted

Why is Cisco enforcing X:X:X:X::X for link-local addresses when the standard says FE80:/10?

The document to which you link claims a specific IOS version. It may be incorrect; that would not be unusual in Cisco documentation. In reality, having tested this on several IOS 15.X versions, you ...
user avatar
  • 94.1k
7 votes
Accepted

How IP helper address works?

Using the ip helper-address command sets up a DHCP relay. DHCP only works on the LAN to which it is connected because it uses broadcast, which cannot cross a router. To remedy that situation, DHCP ...
user avatar
  • 94.1k
7 votes
Accepted

What commands do I run to change IP NAT settings for a Cisco 2800 series router

Simply use the "no" form of the command to remove the first statement, then add the second one. Like this: config t no ip nat inside source static tcp 172.*.*.1 80 117.218.*.* 80 extendable ip nat ...
user avatar
  • 63k
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
Accepted

Cisco show log number of messages

If you’re using ‘show log’ to display messages in the logging buffer, then you’re using IOS or IOS-XE. In both of those Cisco operating systems there is a default syslog buffer size (configured in ...
user avatar
6 votes

How IP helper address works?

To add to Ron's great answer: The key piece of this is that the Router sending the DHCP request on behalf of the client will unicast the request with a source address from the address space the ...
user avatar
  • 636
6 votes
Accepted

EHWIC-1GE-SFP for Cisco 1941

You can change to the SFP interface. Under the interface configuration, configure: media-type sfp To change back to the copper interface: media-type rj45
user avatar
  • 94.1k
6 votes
Accepted

spanning tree RootGuard question on vPC switches

Based on the comments I think you are confused about guard root. You configure guard root on the downstream interfaces of all the switches, except the root switch. Basically, you are trying to protect ...
user avatar
  • 94.1k
6 votes

Why does the Cisco show run command not show the full version, while the show version command does?

To put it in other words... The running-config has a version listed because that's the version of IOS that was used to create/write that config most recently. Every statement in that config should ...
user avatar
  • 655
6 votes

Why does the Cisco show run command not show the full version, while the show version command does?

I would have said the numbers represent different things: show version says "I am running this version", and of necessity has much detail version output in show conf says "This configuration will run ...
user avatar
  • 15.9k
6 votes

How to connect QSFP+ transceiver with MPO connector and SFP+ transceiver with LC connector?

You need a breakout cable - MPO to 8x LC. The reach of the cable depends on the PHY that is used, e.g. 400 m for 10GBASE-SR over OM4, or 10 km for 10GBASE-LR over OS2. Make sure that the transceivers ...
user avatar
  • 71.5k
6 votes

Passive interface default - issue

A passive interface in OSPF does not send hello packets, so it will never form a neighbor relationship nor exchange routes with another OSPF router. By setting the passive interface default command, ...
user avatar
  • 63k

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