Network Engineering Stack Exchange Community Digest

Top new questions this week:

Why is the highest IP address taken as Router ID by default in OSPF?

I know there are 3 ways for Router ID to be selected in OSPF but my question is specific to the auto-select of ID on basis of highest IP address (loopback or non-loopback). Why is the highest IP ...

asked by Orcus Score of 2
answered by Ron Maupin Score of 2

Why is a PoE circuit limited to 328 feet?

I'm trying to learn about PoE and a friend told me the 100 meter limitation on a PoE circuit is because of the DC voltage drop on the power channel, not the data. I had understood the opposite, that ...

ethernet networking power-over-ethernet utp  
asked by Nicknamednick Score of 2
answered by Zac67 Score of 3

How is 65535 bytes is total length of IP datagram?

The maximum size of an IPv4 packet is 65,535 because the Total Length field is a 16-bit unsigned integer, which has a possible 65,536 values (from 0 to 65,535). This created 2 confusions for me. Say ...

ip ipv4  
asked by hibweu Score of 1
answered by Ron Maupin Score of 2

Do PoE lighting systems require a separate network from other PoE systems?

I'm new to networking and PoE but am trying to understand it enough to explain myself. I recently spoke to a Genisys lighting rep who told me their systems couldn't be on the same network as an IP ...

networking power-over-ethernet  
asked by Nicknamednick Score of 1
answered by Zac67 Score of 1

Why shortened version of IP4 exists and it is undocumented but supported everywhere?

For example there is an IP address It is clear that you can use it as the full line, but try that one 192.168.1 It will also work, and it will be automatically converted to ...

ip ipv4 network subnet ip-address  
asked by IGHOR Score of 1
answered by M. Behrens Score of 5

Greatest hits from previous weeks:

dhcp failed. apipa is being used

I'm testing a network and I use the vlan among 20 vlan but in this packet tracer I just use 10 Vlan on my network, In this case, I use the DHCP server on my multilayer switch, not on my router. so ...

vlan dhcp  
asked by Bayu Alam Score of 7
answered by Jatinder Singh Brar Score of 1

How to find the MAC address of a router?

I'm trying to figure out the MAC address of my router. This picture is of using the command ipconfig: This picture is of using the arp -a command: I see it says my IPv4 address is, so ...

router mac-address  
asked by Yoshi24517 Score of 6
answered by TDurden Score of 4

How can hosts on two different VLANs communicate?

It is clear that hosts on two different VLANs can't directly communicate on a single switch, but how do they communicate to each other at all? Do they use a router? How does it work?

routing switch vlan switching  
asked by ds459 Score of 6
answered by Ron Maupin Score of 5

dhcpv6 - stateful VS stateless, what is difference between it?

Can someone explain me, what is difference between DHCPv6 Stateful and Stateless? I was looking on the net and, surprisingly, I found only the remains of information but some general comparison or ...

dhcp dhcpv6  
asked by Paul Score of 8
answered by Eddie Score of 6

Does UDP do anything at all?

It's my understanding that TCP has logic for ensuring reliable communication, but UDP just naively sends information along the channel set up for it using IP and things in lower layers. Does UDP ...

tcp protocol-theory udp transport-protocol layer4  
asked by JacKeown Score of 44
answered by Jeff Wheeler Score of 61

How Can I use "ping command" with source?

I can not use ping 'target' source 'interface' ping source lo0 % Invalid input detected at '^' marker. It's possible if I use "ping" R2#ping Protocol [ip]: ip Target IP address: 192....

cisco ping icmp  
asked by TMoraes Score of 2
answered by YLearn Score of 3

When to choose fiber instead of twisted pair (copper)

These days both fibre and twisted pair are supporting 1000BASE-T and 10GBASE-T, but when do you choose one over the other? The obvious one is maximum cable length, but what are other factors which ...

ethernet fiber cabling  
asked by Lucas Kauffman Score of 85
answered by Chris Travers Score of 68
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