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 ...
- 1,636
14
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 ...
- 67.1k
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 ...
- 27.2k
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 ...
- 19.5k
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 ...
- 98.7k
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 ...
- 4,690
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 In that function, it's now been pretty much superseded by the similar SHA256-crypt and ...
- 408
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. ...
- 98.7k
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 ...
- 19.5k
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 ...
- 1,949
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 "...
- 2,416
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/...
- 3,754
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....
- 98.7k
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:
...
- 98.7k
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 ...
- 98.7k
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 ...
- 98.7k
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 ...
- 98.7k
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 ...
- 67.1k
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.
...
- 29.8k
7
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 ...
- 98.7k
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 ...
- 29.8k
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 ...
- 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
- 98.7k
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 ...
- 705
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 ...
- 16.2k
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 ...
- 82.6k
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, ...
- 67.1k
5
votes
Cisco - Changing LACP rate from slow to fast
Based on my tests changing the LACP rate bounces the Port-Channel:
*Jan 6 04:08:08.204: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/15, changed state to down
*Jan 6 04:08:08....
- 51
5
votes
Accepted
How do I remove a vlan from a trunked port
In Cisco devices you can do the command with no in front of it: no switchport access vlan 12.
Putting the access VLAN on a trunk port does nothing unless the trunk goes down and the port reverts to ...
- 98.7k
Only top scored, non community-wiki answers of a minimum length are eligible