Most Popular
1500 questions
17
votes
8 answers
When *not* to create a SVI for a L2 VLAN?
When creating VLANs for just L2 on a switch -- routing will be handled by a device within that VLAN such as a load-balancer -- it isn't necessary to create the vlan interface. As a matter of habit, I always create the interface anyway-- no IP…
generalnetworkerror
- 7,104
- 6
- 32
- 66
17
votes
5 answers
Why do we need ports with IPv6?
My understanding is there are 2^32 - 1 possible IPv4 addresses, and 2^16 - 1 possible ports. Which gives ~2^48 addresses.
The additional 2^16 additional ports seem almost insignificant considering the IPv6 address space is 2^80 times larger than the…
Josh
- 273
- 2
- 6
17
votes
3 answers
Why does one say IP fragmentation is bad and to be avoided when in reality data always needs to be fragmented for MTU compatibility?
Why does one say fragmentation is bad and must be avoided due to performance issues when in reality fragmentation intrinsically occurs within the communication ?
Example:
User1 wants to send 100 000 bytes to User2
Maximum MTU size of the network…
Floji
- 319
- 2
- 5
17
votes
4 answers
Confusing A, B, C network classes
I'm studying IPv4 addresses and came across this whole thing about classful addressing. I get the idea behind it, bit there is something I find confusing:
There are two "ABC" ranges:
First one:
A: 1.0.0.0 to 126.0.0.0 with /8
B: 128.0.0.0 to…
Axel Kennedal
- 671
- 4
- 9
- 16
17
votes
2 answers
What is the difference between Ethernet II and 802.3 Ethernet?
Can anyone explain to me what is the difference between Ethernet, Ethernet-II and 802.3 Ethernet.
I referred to a lot of books, they are in high level language. Can anyone explain to me in a simple manner?
user2720323
- 1,611
- 9
- 20
- 26
17
votes
5 answers
How to choose a BGP router ID when using IPv6 only?
Usually, when using BGP, you can choose (or your device chooses four you) a router ID from one of your assigned public IP addresses.
Now, let's admit you only run IPv6. As the router ID is still a 32 bits number, it can not be copied from a…
Benjamin A.
- 1,697
- 2
- 15
- 27
17
votes
3 answers
On which layer of the OSI Model does the arp protocol belong?
Can anyone explain which layer of the OSI model ARP belongs to and which socket it uses?
I referred to lots of books before asking this question.
In some books, Authors are saying that it belongs to the datalink layer, in some they say it belongs to…
user2720323
- 1,611
- 9
- 20
- 26
17
votes
2 answers
Why don't we use MAC address instead of IP for having "Internet" or doing communication?
We know MAC address is unique in each devices.So why can't we just send/receive data using MAC address only?
Tanvir Rahman
- 295
- 2
- 3
- 8
17
votes
3 answers
How to verify that a UDP port is open?
I have here a dilemma. I have a device that communicates to another remote device but there is a firewall between them. It's a UDP connection, so TCP utilities don't work to test if the specific port is open. I know that we could get that from the…
JoeliNNaBit
- 171
- 1
- 1
- 4
17
votes
3 answers
Backing up Cisco router configuration - including ssh keys
We have some Cisco 2821, 2921 and 1921 routers in our shop. I can back up and restore the configurations by copying out or in the startup-config file, but what about the keys for ssh? I don't want them to change in case I have to swap in a new…
J. L. Tympanum
- 417
- 1
- 4
- 7
17
votes
3 answers
Is it possible to remotely influence BGP localpref?
A colleague is attempting to implement active/passive internet multihoming. The design entails sending communities (listed below) to the passive provider to lower the local preference at remote ASes for the advertised routes. The documentation…
Dennis Olvany
- 2,435
- 1
- 17
- 34
17
votes
6 answers
What's the difference between an Ethernet cable and a UTP cable?
Is there such a thing as an Ethernet cable or technically no? Are they actually called UTP cables?
From wikipedia
UTP cables are found in many Ethernet networks and telephone systems.
Celeritas
- 835
- 4
- 11
- 18
16
votes
7 answers
What are the differences between VRRP and HSRP?
Are there any significant differences between VRRP and HSRP?
Bulki
- 2,383
- 7
- 25
- 44
16
votes
12 answers
What would cause high latency anytime there is traffic on WAN?
I have a network that has been experiencing slow internet speeds. After a great deal of troubleshooting, I have determined that any streaming content/downloads will cause the latency of WAN traffic to explode.
For example, under no load, I ping…
Blackjack00
- 297
- 2
- 3
- 4
16
votes
3 answers
How come SFP modules are so incompatible?
In theory I like the SFP concept very much. However what strikes me is the manufacturer restrictions for every switch/card. How come different SFP modules work with different vendors only? Is there a design flaw in the SFP specification? What makes…
Thomas
- 269
- 2
- 6