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8
votes
1answer
1k views

UDP hole punching NAT port

I just read an article about the process of "punching holes" with the UDP protocol. I understand how it's done, but I have one last question to clear up things. We have the rendezvous server and ...
19
votes
2answers
23k views

Ethernet autonegotiation differences between (10M | 100M | 1G) Ethernet

I am studying for CCNA and on Wendell Odom's book is said that(regarding autonegotiation): When autonegotiation fails on one node, to choose (half/full-duplex) we must use the rule: If you have a 10/...
10
votes
2answers
4k views

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

Alright - been battling this for at least 20 hours consecutive.. Sorry if this seems like a long rant, or a blog post, but I'm getting to the point of exhaustion. So, here's the deal. We're using ...
6
votes
2answers
550 views

VLAN-Subnets 1:1?

I often hear people saying that each VLAN is a subnet (or is associated with a subnet) but is that really true? Assume I have 10 big offices. I will have a subnet for each office but only 2 VLANs ...
4
votes
4answers
2k views

Can IP packet with TTL=1 reach loopback interface of a switch?

This is a question that bothers me a lot. And I cannot argue with colleagues because all switches I see can response the ping request even my TTL=1. So my question is, does TTL decrease between ...
3
votes
1answer
1k views

Can a 172.168.10.0/28 be a class B Subnet

I am starting my studies in networking and starting off with the basics of IP addressing and Subnetting with CIDR values. My Question here is 1st how can you tell the subnet class of an IP address ...
3
votes
1answer
396 views

How does a router know to which PC in a network to send a response from a server?

When my PC sends a request to a server, the transmitted IP address is the one of my private network. When the server responds to the request, how does the router know to which PC in the network to ...
33
votes
2answers
80k views

What is the actual size of an Ethernet MTU

I think I might be getting confused with terminology surrounding MTU. This definition from Wendell Odom's CCNA book on MTU: The IEEE 802.3 specification limits the data portion of the 802.3 frame ...
13
votes
3answers
37k views

On which layer of the OSI Model does the arp protocol belong? [closed]

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 ...
33
votes
3answers
98k views

What is the difference between MSS and MTU?

I'm confused as to the difference between maximum segment size and a maximum transmission unit. Can someone please explain in relation to layers 2 and 3? If I had a packet of 800 bytes in the ...
18
votes
4answers
21k views

Why does WLAN use Collision Avoidance and not Collison detection?

I am searching for this answer for quite some time now. Why there is CSMA/CD in LAN but CSMA/CA in WLAN? The best explanation I could find is "due to extreme ratio in transmitting and receiving power,...
7
votes
3answers
4k views

Does a switch understand packets? If yes, what is the frame terminology for?

I was a little confused between packet and frame. The confusion was based on, if a switch is a layer 2 device, how does it reads a packet from a layer 3 device, and where is the 'frame' thing which is ...
14
votes
6answers
23k views

How are IP addresses mapped to MAC addresses?

I've been reading about the differences between MAC and IP addresses, and why we need both of them. To summarize, MAC addresses are physical unchangeable unique IDs for every single device while IP ...
12
votes
1answer
23k views

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 ...
7
votes
1answer
4k views

How can a TCP window size be allowed to be larger than the maximum size of an ethernet packet?

I know that TCP window sizes can be scaled to over 64KB, but looking at an ethernet packet datagram, such as this one: it looks like a layer 2 packet is limited in size to be much smaller than that. ...
21
votes
3answers
8k views

Exactly when is PMTUD performed? (Path MTU discovery)

In discussions that have spurred from other questions on this site, I've realised that I don't have a solid understanding of when Path MTU Discovery (PMTUD) is performed. I know what it does -- ...
13
votes
4answers
5k views

/31 Point-to-point bitmasks

When is it appropriate to use a /31 network in production, and is using them considered good practice? On a point-to-point link, broadcasts shouldn't be required, so is there any compelling case for ...
12
votes
3answers
2k views

Is there such thing as a network bridge?

Is there such a thing as a network bridge or is it always meant as a switch implementing a bridging function? Whilst bridges are described as devices that create separate collision domains in network ...
12
votes
5answers
9k views

When is BGP needed?

I have a question about BGP. When exactly is BGP needed? I remember reading that BGP is needed for communication between autonomous systems, but is this always true? For example, in packet tracer I ...
15
votes
2answers
8k views

In which OSI/TCP-IP model layers do BGP, RIP protocols belong?

We know that in the OSI or TCP-IP model, the higher layer utilizes the services offered by the lower layer. For example, the data link layer uses services offered by the physical layer, network layer ...
14
votes
2answers
12k views

Why does “show interface” show “Last input never” when packets input is incrementing?

Why is it that when I perform a show interface command I see that Last input always shows never? FastEthernet1/31 is up, line protocol is up (connected) Hardware is C6k 100Mb 802.3, address is 000d....
14
votes
4answers
14k views

What's the difference between `Latency` and `Round Trip Time`?

Golang community provide a HTTP/2 demo website to compare the performance between HTTP 1.1 and HTTP/2. We can choose different latency, e.g. 0s latency, 30 ms latency, 200ms latency. Is latency a ...
9
votes
4answers
1k views

What Exactly is SDN?

Is SDN a buzzword or is it a protocol, standard, or recommendation? What differentiates SDN from VMware NSX, for example?
9
votes
3answers
1k views

What is a “Layer 3 Switch”?

What is a "Layer 3 Switch"? I essentially understand the OSI model, well maybe I don't and maybe that is why I don't understand. Its just that I don't see how/when/if a "managed switch" becomes a "...
8
votes
1answer
2k views

Staging Many Lightweight Cisco AP's for Deployment

My organization is soon going to be deploying approximately 600 new Cisco 2602i access points in a CAPWAP deployment with several 5508 controllers. This is an infrastructure refresh; currently we ...
8
votes
7answers
19k views

Juniper EX-series: How can I transfer a config from one switch to another?

I have a lab EX-2200 that has a config on it that I now want to replicate onto four more EX-2200's... I'm sure there's probably an easy way to do this, but couldn't find it on the Juniper KB or by (a ...
3
votes
1answer
2k views

minimum hop limit for a packet where there are n routers between source and destination

I am having some confusion while calculating he minimum hop limit ... consider following scenario: (source)-------(R1)--------(R2)--------(destination) Now when an IP datagram is supposed to travel ...
3
votes
1answer
2k views

Traceroute UDP port question

I know, that traceroute uses UDP, and for destination port it starts with 33434. Then, with each next hop it increments the destination port number by 1. The questions is: why does traceroute need to ...
16
votes
5answers
8k views

Speed of Light in Copper VS Fiber - Why is Fiber Better?

I'm reading Computer Networks - A Systems Approach 5th ed., and I came across the following statistics for the speed of light through different mediums: Copper – 2.3 × 108 m/s Fiber – 2.0 × 108 m/s ...
14
votes
4answers
1k views

Is a wireless only network (for end users) a viable option?

We are constructing a new building, and our CIO is pushing for a solution where he doesn't have to spend the money on copper runs to all the user stations and wants to use wireless only for this ...
13
votes
1answer
1k views

What happened to IPv5?

I hear/read much about IPv4 and IPv6 and nothing about IPv5. Where did it get lost in the discussion?
12
votes
7answers
13k views

DHCP relay problem on interfaces secondary network

A secondary network was configured on an interface of a Cisco 2621 router and the ip helper-address commands put in place but no clients of that secondary network could pull DHCP addresses. We swapped ...
10
votes
1answer
313 views

Is a FIN only segment legal?

It would be convenient to mark TCP segments with just the FIN flag set, as an intrusion (without tracking the reply). I have always assumed that a FIN without an ACK, while rude and rare, is legal, ...
10
votes
3answers
4k views

Inbound BGP load-balancing from same ISP router

I have two BGP routers for DIA with an issue with one provider in that the two links to this provider land on the same SP router. My ethernet handoffs via two separate MetroE links from another ...
9
votes
1answer
13k views

ProCurve CPU at 100% for several minutes after reboot

I have been doing firmware upgrades in HP switches. Two different models have been upgraded: ProCurve Switch 5406zl Intelligent Edge (J8697A): upgraded from K.15.06.0008 to K.15.12.0012 HP 2520-24G-...
9
votes
4answers
3k views

Switch interface config for IP Phones

I have seen both of the following methods of switch interface configuration for supporting IP Phones. switchport access vlan <data-vlan> switchport voice vlan <voice-vlan> switchport ...
7
votes
4answers
3k views

Why is a TCP Socket identified by a 4 tuple?

Newbie to networking here. I'm reading the Computer Networking (3rd edition) book, and in section 3.2 they are discussing multiplexing / demultiplexing for both UDP and TCP. In the UDP protocol, a ...
7
votes
3answers
3k views

How does NAT decide which connections are inbound, and which are outbound?

I'm building a P2P application that needs to be able to access nodes behind a NAT. This NAT does not allow inbound connections, therefore the nodes outside the network cannot reach out to the nodes ...
6
votes
2answers
3k views

Why do LANs use MAC addressing instead of IP addressing?

Why do LANs use MAC addressing instead of IP addressing? In other words, why can't a network just assign an IP address to a local area network device and send the data to that, instead of the MAC ...
6
votes
1answer
1k views

Why can I ping IP addresses from 127.0.0.1 to 127.255.255.254?

I thought that the loopback IP address of my machine is 127.0.0.1. I do not understand why am I able to ping IP addresses until 127.255.255.254.
6
votes
1answer
5k views

ARP request unicast MAC?

I would like to ask, with ARP request I got to believe that the destination MAC address was in all situations a broadcast address. Yet I got across a wireshark capture: I just cannot understand the ...
6
votes
1answer
1k views

subnetting is incorrect in show ip route output

in one of the CCNA courses theres the following image taken from a routing table: I'm not very confident with my subnetting skills, so please confirm if I'm wrong: 172 is a class B network (/16). So ...
6
votes
1answer
289 views

Why do we have authentication before association in 802.11

Why does client authenticate before associating with the AP. What does open system authentication even achieve. I fail get an accurate reason from my web searches. Best reason I do get is unlike wired ...
5
votes
2answers
4k views

How does a layer-2 switch work with UDP?

If UDP and/or TCP send packets via IP to an Internet Protocol Address, how can a layer-2 switch forward these? Is this possible or do you need a layer-3 switch?
5
votes
1answer
1k views

Juniper destination based CoS

I'm trying to do destination based CoS on Juniper MX basing on destination ASN. I've tried config below. set policy-options as-path BGP-PATH-TO-MARK-COS "65512 .* set policy-options policy-statement ...
5
votes
1answer
1k views

What is the reason for the different order of the Source and Destination in a L2 header?

A TCP/UDP header (Layer 4) lists the Source Port, then the Destination Port: An IP header (Layer 3) lists the Source IP, then the Destination IP: An Ethernet header (L2) and a WiFi Header (L2) lists ...
4
votes
2answers
3k views

Why do multi-line crypto ACL's create instability in VPN tunnels?

Why does using multiple sets of specific ip's to specific ip's in a crypto ACL - cause instability in VPN tunnels, please relate this to phase 2 SA's (IPSEC). Ex. 172.16.0.0 -> 10.0.0.0 172.17.0....
3
votes
4answers
154 views

Need of routers and IP addresses

I dont know if my research is enough or not but I could not find answers on the net. My question is why not use bridges instead of routers. We know bridges can connect two different networks. Using ...
3
votes
4answers
35k views

What is the difference between smart vs managed switch?

I want to buy a new switch to replace an old one which is unmanaged and I see that there are smart and managed switches.. what it the difference?
1
vote
2answers
214 views

Does the same IP cause IP conflict if one is from /22 other is from /24?

I have two hosts. They both have the same IP/subnet, ex.: 1.2.3.4/24 on both. I know this is bad, since there will be duplicate IP in the network. OK. But: If I have different (?) ranges: 1.2.3.4/...

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