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Questions tagged [routing]

For questions about routing, the process of selecting to which network path traffic is sent. Consider using a more specific tag if your question is about a routing protocol like BGP or OSPF.

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NAT Overlapping

I am trying to do some networking lab. Basically, I have a network like this: So, is it possible to configure NAT router in such way, that PC1 and PC2 can access remote HOST and each other. The ...
mcferden's user avatar
  • 173
25 votes
4 answers
76k views

Why must all areas connect to an Area 0 backbone in OSPF?

This question is a literal repost of the same question asked on The Cisco Support Community. Answers are unique to Stack Exchange. Why is area 0 the backbone area in OSPF? Why must all other areas ...
Trojan's user avatar
  • 1,418
2 votes
3 answers
396 views

Is an entirely decentralised peer-to-peer network feasible? How far could it be scaled?

Most of the reading I've done about P2P networks are either about small scale simple mesh networks, where every peer can talk to another, or about high level protocols such as bittorrent, where data ...
Tom's user avatar
  • 123
19 votes
2 answers
9k views

How does the router know how to route the packets to my terminal?

Suppose I have a network of 2 computers, each having a private network address of 192.168.1.101 and 192.106.1.102. For my public ip address, it is 10.2.10.172. When I make a http request to google....
Mc Kevin's user avatar
  • 301
16 votes
5 answers
16k 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 ...
Artur's user avatar
  • 317
26 votes
7 answers
11k views

Does CIDR really "do away" with IP address classes?

I am still struggling to understand to what extent CIDR really renders IP address classes obsolete. Here's what I understood so far: It's ridiculously inefficient (and impossible, too) to assign ...
user avatar
15 votes
3 answers
23k views

MPLS vs Encrypted VPNs - traffic security?

Why do people say a lot of times that they have two connections between two offices - the main one being over MPLS and the backup one over VPN. Why not run a VPN over MPLS too? Is MPLS secure? Can no ...
Yon's user avatar
  • 253
9 votes
3 answers
8k views

How are MAC/IP addresses used in routing

I have to teach my sixth form about MAC Addresses and IP Addresses in a few weeks time and there are some areas I am unclear on which I am hoping some of you will be able to clarify for me. I have ...
Robert Flook's user avatar
7 votes
4 answers
88k views

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?
ds459's user avatar
  • 353
6 votes
2 answers
771 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 ...
Pietros's user avatar
  • 121
3 votes
4 answers
432 views

Do all network devices need to make routing decisions, regardless of communication across networks or within a network?

From Hunt's TCP/IP Network Adminstration: Gateways route data between networks, but all network devices, hosts as well as gateways, must make routing decisions. Is it correct that routing ...
Tim's user avatar
  • 1,555
21 votes
4 answers
25k views

Risks of using non-private IP addresses internally?

My company has received a large industrial machine with many networked devices on it. Unfortunately the engineer in charge has used a public IP address range on the machine. I'm in Europe. The chosen ...
Transistor's user avatar
18 votes
2 answers
14k 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 ...
Mahesha999's user avatar
12 votes
1 answer
14k views

How is BGP "AS_SET" used?

RFC 1771 defines a path attribute type of AS_PATH as follows: AS_PATH (Type Code 2): AS_PATH is a well-known mandatory attribute that is composed of a sequence of AS path segments. Each AS path ...
Eddie's user avatar
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10 votes
3 answers
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 ...
generalnetworkerror's user avatar
10 votes
1 answer
4k views

How does NAT share one public IPv4 address across multiple private IPv4 addresses [closed]

I think it's a very classical question, but, thought I've have some background, I don't have enough vocabulary anymore to search and understand correctly in the Web. Let's say I have a home network ...
Nicolas Zozol's user avatar
9 votes
1 answer
7k views

Static routes: numerical next-hop vs interface

I'm reviewing old Cisco modules, and in CCNA 2, Module 2.5.1.2, it states, Under certain conditions, the network administrator will not want to configure the static route with an exit interface but ...
user avatar
7 votes
2 answers
3k views

IPv6 and online privacy and security

I am studying up on IPv6 and part of the talk was about how the machines generate or can have multiple IPv6 addresses for internal use and external use. Does this mean that there is no longer a "...
Jason's user avatar
  • 1,015
7 votes
6 answers
35k views

Difference between routing, forwarding, and switching

I feel like the three terms are often used as synonyms but actually all mean something different. I did look at Wikipedia sites but I'm still unsure about the definitions of the three. From my ...
stefanbschneider's user avatar
7 votes
2 answers
7k views

Dell PowerConnect 5524 VLAN routing

I have a Dell PowerConnect 5524 that I'm trying to configure. What I want is simple routing between VLANs and the user guide is less than helpful. On page 220, it says (or implies) that all you need ...
Sean Airey's user avatar
6 votes
1 answer
3k views

NX-OS 9.3: ECMP polarization and "ip load-sharing ... rotate"

This is a "why and how exactly does this work" question. The given problem is already solved. QUESTION: I'm interested to understand what "rotate" in ip load-sharing address source-...
Marc 'netztier' Luethi's user avatar
5 votes
3 answers
5k views

Does a router send frames or packets?

Perhaps it's a novice question, but does a router send/receive frames? When I read about this subject, it seems that routers decapsulate the frame on arrival, and encapsulate the packet in a frame in ...
Smbbo's user avatar
  • 51
5 votes
1 answer
542 views

Who decided the Admin Distance Values for each protocol?

OSPF has an administrative distance of 110 EIGRP has an administrative distance of 90 RIP has an administrative distance of 120 But where did 110, 90, and 120 come from? Who or what entity decided ...
Eddie's user avatar
  • 15.1k
3 votes
1 answer
3k views

What is the point of a subnet mask on a local network?

I have a question regarding subnet masks and my understanding (or misunderstanding of them). So when a subnet mask is used, a bitwise AND is performed using the subnet mask and the IP address(es). ...
Robert Flook's user avatar
3 votes
1 answer
638 views

Cisco Prefix List Won't Appear in Route Table

I have the following prefix-list configured on our router: ip prefix-list adsvr seq 5 permit 172.30.5.241/32 ip prefix-list adsvr seq 10 permit 134.239.130.143/32 ip prefix-list adsvr seq 15 permit ...
cpatte7372's user avatar
3 votes
2 answers
3k 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 ...
manifold's user avatar
  • 133
3 votes
3 answers
7k views

At which layer does router operate?

I have studied from various sources that router is a layer 3 device. It does routing based on Network layer (layer 3) header, but I have a doubt. Network address translation (NAT) is a feature of ...
Raja's user avatar
  • 355
2 votes
2 answers
597 views

CGN and its advantages

I have been reading about CGN. Though similar to NAT it is used by service providers to route traffic without the need for the a public IP address. But when the packet leaves the ISP to the public ...
john 's user avatar
  • 1,237
2 votes
3 answers
358 views

Routing with private addresses

Let's say that we have a private network, with private addresses and a NAT enabled router at the end. If the router is misconfigured and routes traffic to the global internet, keeping as source ...
konstantinosAR's user avatar
2 votes
2 answers
19k views

What is nodal delay?

I keep seeing the definition of nodal processing delay as "The time it takes to process a packet in a network node (router, switch, hub, etc.), which is dependent on the speed of the device and ...
Celeritas's user avatar
  • 835
2 votes
2 answers
582 views

Static Routes and selection

For what I know, Static Routes don't have a Metric. So, what if a Router has more than one Static Route to a Network? Let's say that on the topology below we have Static Routes configured, and R1 can ...
artib's user avatar
  • 21
2 votes
2 answers
5k views

What is the election process of Router ID in OSPF?

I am a little confused on the process OSPF uses to select the Router ID. Is following correct for the selection of the router ID in OSPF? Manual configuration Highest IP address on a loopback ...
Joe's user avatar
  • 21
1 vote
1 answer
812 views

BGP Best Path Selection Algorithm

According to this cisco document (https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13753-25.html), shortest AS_PATH is the #4 algorithm in the sequence to evaluate, out of 13 ...
Rafiq's user avatar
  • 121
1 vote
1 answer
134 views

Best path in BGP Routing

Assuming 'Network A' is having 2 ISPs which are directly connected to 'Network B', which path will be used to connect to 'Network B'? Network A --> IP Transit A / IP Transit B --> Network B
Anson's user avatar
  • 13
1 vote
1 answer
1k views

Why does OSPF use flooding instead of broadcasting?

In flooding, we send unicast/multicast frames to all the routers in the network, whereas in broadcasting, we have a broadcast address by which we send packets to all the routers. In OSPF, "Router ...
Zephyr's user avatar
  • 441
47 votes
8 answers
4k views

Network Neutrality, how does it actually work, technically speaking?

In this NPR article there is mentioned 'network neutrality' with very little details on what it actually is or how it actually works. I tried researching it on my own but I get a lot of non-technical ...
Matthew Peters's user avatar
40 votes
8 answers
34k views

How would a router with /32 WAN subnet mask communicate with the rest of the Internet?

I'm studying networking and one of the most basic things I've been told countless times is that computers can't communicate outside of their own subnet. On the other hand, by looking at some ADSL ...
AndrejaKo's user avatar
  • 695
24 votes
7 answers
59k views

Why use iBGP inside an Autonomous System, if IGP protocols fulfill the need for internal communication

Can anyone explain why we need iBGP for the routes when we have the IGP protocols (OSPF, RIP) for internal communication within the AS? I have read a lot of articles and books, but I could not find ...
user2720323's user avatar
  • 1,611
23 votes
7 answers
41k views

Difference between access list and prefix list?

Can someone explain with an example whats the difference between an access list and prefix list.
NAVEEN GEORGE's user avatar
21 votes
3 answers
4k views

CEF operations on L3 switch vs router

I understand that L3 switches use CEF for faster packet forwarding. However, CEF will not work for packets that need to undergo NAT. Does this mean CEF isn't used by edge routers and edge L3 switches? ...
Michael May's user avatar
  • 1,005
20 votes
9 answers
15k views

Why are IP addresses given to each interface and not device? What would the implications of that be?

Why do we need to give IP addresses to each interface? Wouldn't giving one to each device be enough?
Tiago Oliveira's user avatar
16 votes
7 answers
111k views

What are the differences between VRRP and HSRP?

Are there any significant differences between VRRP and HSRP?
Bulki's user avatar
  • 2,393
14 votes
1 answer
35k views

RIB vs FIB differences?

Can someone explain the differences between a RIB and FIB a little further? I didn't see any similar questions on the site so I thought this would be a good addition. The RIB routes and the FIB ...
stets's user avatar
  • 1,040
14 votes
2 answers
11k views

What is a non-portable IPv4 address block?

For example, a Whois query for 4.4.4.0 says: ADDRESSES WITHIN THIS BLOCK ARE NON-PORTABLE Does the owner simply declare the block or a subnet are not up for sale? Or does non-portable have a ...
user2964971's user avatar
13 votes
3 answers
12k views

OSPF Stuck in Exstart Adjacency State

According to this article two routers will get stuck in the exstart adjacency state when their configured MTU sizes do not match. Does a VLAN tag affect this as well even if the routers involved are ...
JDGray's user avatar
  • 311
13 votes
5 answers
15k views

Why does OSPF need Type2 LSAs?

Learning more about OSPF for CCNP studies. I'm looking at how OSPF builds its links, and have just covered Type1 LSAs. Looking at Type1 LSAs, I'm wondering why these are even necessary? The book ...
A L's user avatar
  • 3,310
11 votes
3 answers
34k views

Whats's the function of a loopback interface in routing protocols?

So I've got this task where I have to setup a virtual network with an OSPF routing protocol. I firstly ignored this loopback interface I had to configure on the routers since it didn't do any ...
iPh1ps99's user avatar
  • 153
10 votes
3 answers
27k views

OSPF or iBGP for interior routing protocol?

So the plan is, two core routers each with a eBGP session to one of two ISPs with full routes. Both routers publish their full tables to each other so they can control traffic flow more intelligently ...
OJS's user avatar
  • 343
9 votes
1 answer
641 views

How to provide failover for space-diversity T1

I have inherited a small, insular, dedicated network which is essentially trouble-free, so naturally I want to improve it :-) I lowered my network knowledge and savvy to somewhere around a 2 to 3 on ...
Bote Man's user avatar
9 votes
3 answers
5k views

Cisco NAT hairpinning

I have a Cisco router configured NAT (4 static NAT and dynamic NAT). My problem is that I can't access internal servers using public IP addresses from the internal network. I know what the problem ...
sareeshmnair's user avatar