Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [router]

For questions about network routers, devices that forward data packets between computer networks, commonly at the network layer (layer 3) of the OSI model.

8
votes
3answers
3k 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 ...
8
votes
2answers
2k views

What do these three options in a Cisco Router NAT configuration mean?

In a standard Static PAT configuration, where one IP:Port combination is always mapped to another IP:Port combination, there are three possible combinations of inside/outside/source/destination that ...
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 "...
11
votes
7answers
12k 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 ...
3
votes
4answers
141 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 ...
1
vote
1answer
3k views

HSRP issue both device active stats

Here is the Diagram. Ip address: ISP: [VIP]- 10.107.25.5 [R1] - 10.107.25.6 [R2] - 10.107.25.7 Me: [VIP] - 10.107.25.10 [SW1] - 10.107.25.11 [SW2] - 10.107.25.12 Configuration on port: SW1 ...
16
votes
4answers
40k views

Bad Mask for IP Address Error

I'm not too clear on subnetting rules and experienced an error when I tried to assign 148.26.1.176/28 to an interface on my Cisco router. Can someone please explain why it was not allowing me to ...
9
votes
3answers
17k views

Assign an IP address based on switch port

Short: I want DHCP server to assign a preconfigured IP address based on a port (on a switch, ideally) a device is connected to. Long: My situation: I am building an automated indoor farm (for ...
6
votes
2answers
5k views

Change Ping Response for Traffic Blocked by Access Control List

I am trying to ping a host, let's say 10.1.1.1, from 20.1.1.1. I have created the ACL: R1(config)#access-list 1 R1(config)#Deny 20.1.1.1 R1(config)#Permit any R1(config)# int s0/0 R1(config-if)#ip ...
5
votes
1answer
837 views

Why are routers not answering ARP Broadcasts?

Host A wants to send something to Host B who is in a different network. Between them is Router 1. Host A sends an ARP broadcast but Router 1 is not answering it. Why is that so?
3
votes
1answer
527 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). ...
3
votes
2answers
4k views

Should I increase the timeout value for UDP on our VPN router-device?

We have a SonicWALL NSA 2400. We have numerous (100+) personnel in different offices in different physical locations that establish VPN sessions successfully every day. Some of these client computers ...
3
votes
2answers
193 views

How to understand the output below from BGP?

I don't understand some data of the show route: admin@MX-RE0# run show route 36.250.236.6 inet.0: 736608 destinations, 806660 routes (736608 active, 0 holddown, 7 hidden) + = Active Route, - = Last ...
22
votes
4answers
44k 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 ...
12
votes
5answers
14k 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 ...
10
votes
4answers
3k views

how to get scp via snmp to work with cisco routers?

I have a lab setup where I'm trying to use SCP via SNMP to a cisco router.I found some online documentation such as: http://ccie20728.wordpress.com/2008/05/20/get-the-cisco-configuration-over-snmp/ ...
12
votes
3answers
11k 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 ...
8
votes
1answer
2k views

Something is filling my force10 ARP table

I have 2 force10 s25 switches that are used for a dark fiber link between two school buildings. One of my switches is filling its ARP table to the brim and then failing. This can happen as often as ...
8
votes
3answers
2k 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 ...
6
votes
2answers
536 views

MPLS can reroute, but can it route?

I have 4 Cisco routers, connected one to another like the following: **R1**(s1/0)--(s1/0)**R2**(s1/1)--(s1/0)**R3**(s1/1)--(s1/0)**R4** All of them have an IP address assigned on their interfaces. ...
5
votes
2answers
3k views

Can a network with a default gateway successfully ping a PC in another network without gateway?

Please see the picture first. Let someone ping from PC1 to PC2 (which has no default gateway). Would it be possible for the ping to successfully reach to PC2 and then come back in the fashion ...
10
votes
4answers
16k views

Setting up DHCP server on the router or on the switch?

We're using the Cisco 1921/K9 with a SG300 L3 switch. Does one set up DHCP server on the router or on the SG300? If both is capable, what is the reason to choose one over the other? Note: I have 4 ...
9
votes
2answers
2k views

Differences and functions of type codes 0800 and 0806

What are the primary differences and functions (or applications) of type codes 0800 and 0806? Through my own research, I found the 0800 was related to the 0800 to the IP/Layer 3 of the OSI model. ...
5
votes
2answers
3k views

How does router prevent Broadcast radiation

I just learned networking and according to a wiki article on broadcast radiation prevention, it says: Filtering broadcasts by Layer 3 equipment, typically routers (and even switches that employ ...
4
votes
3answers
23k views

Load balancing with multiple ISP, two routers and firewall

I have two ISP connections on two Cisco 2901 routers, in front of Cisco ASA-5515 firewall. I need to configure failover load balancing network. Two Cisco 2901 router with dual (different ISP) ...
3
votes
1answer
250 views

Could launching a virtual router with less-than-recommened RAM cause interfaces to not initialize?

I'm trying to launch a few vSRX devices through GNS3 (and VirtualBox). The issue that I'm running into (I think) is that my interfaces seem to not properly initialize if I don't start the instances ...
2
votes
1answer
55 views

Multiple routers with one long range antenna

Wifi routers have a limit on the number of clients that can connect, Assuming i have many routers and i connect them together via wireless bridge, then i connect one single long-range antenna that ...
2
votes
4answers
6k views

How does ARP work between two routers?

When ARP is used by a host in a LAN, then it is broadcast because the host does not know where is the destination host, but a router knows which interface it must use to get to the next router. Then ...
12
votes
1answer
2k views

Can a router send ARP requests to hosts?

I play with libpcap in C recently to create an arp sniffer program that captures arp requests on the air. I came up with a strange effect. I captured arp requests from my router. I don't know if this ...
6
votes
4answers
2k views

Advantage of layer 3 switch over Router

What is the advantage of Layer 3 switch over the Router ??
6
votes
2answers
1k views

How to monitor SPAN port for a routed port on 3560G

Is configuring the SPAN port same for a routed port vs a switch port? I have a routed port on my layer-3 3560G for which I need to configure SPAN and capture packets ingress and egress for ...
6
votes
1answer
3k views

console connection via Cisco router's AUX port

my question is simple: if I am logged into a Cisco router via console or ethernet in priviledged mode, is there a command to initiate a connection through the local AUX port to a nearby console port ...
5
votes
4answers
9k views

Cisco Router Limiting Bandwidth

I have a Cisco 2621XM connected straight to my ISP modem. I have a computer on the second interface of the router. Topology: ISP -> Modem -> Cisco Router -> Computer When I run a ...
5
votes
1answer
444 views

Switch FIB and router FIB

Forwarding Information Base (FIB) also called Forwarding Table or Mac Table according to wikipedia. I first explain my understanding of the FIB in both Switch and Router. Does not hesitate to correct ...
5
votes
6answers
608 views

Can the same network IPs be used more than once

Because of how routers separate networks is it possible to say use the network 192.168.1.0/24 several times as long as you have enough networks to separate? Example: 192.168.1.0/24 <--> 172.16.0....
5
votes
2answers
8k views

ISP edge router configuration

I need to configure Cisco 2901 router to route between interconnect block and usable ip block. Circuit is fiber 30Mb/s I got this info from ISP provider: IP space: Interconnect block - 50.204.xxx.80/...
5
votes
1answer
39k views

Why is my Router's WAN IP different from public IP?

My Router's WAN IP is a public IP - 172.100.x.x And my public IP is - 182.x.x.x Why do I have 2 public IP's? Does this probably mean that my router is behind another router? But then what is the use ...
5
votes
2answers
2k views

Network Gateways vs Interfaces

When looking at the contents of a routing table section on the Wikipedia article on Routing Tables, it contains a table as an example of a routing table with two headings which have an unclear ...
4
votes
4answers
601 views

Is there a valid scenario where a router is used to translate a public IP address?

NAT typically refers to router translating an IP address from a private network to a public IP address so that the node on the private network can access public Internet. Is there a valid scenario ...
4
votes
3answers
659 views

How does a router a layer 3 device translate port address in PAT, as it is a layer 3 device?

While I was reading about PAT i.e Port Address Translation.The router was configured to translate all the private IP addresses to one single public IP.Since router is a layer-3 device, it can do that ...
4
votes
1answer
2k views

Screen to Junos “Set route …” command

tell me please how to translate the following Screenos to Junos... Do I understand correctly that the path to route 80.70.128.142/32 is via vrouter "UntrustGi-vr" ? Screenos command: set vrouter "...
4
votes
1answer
523 views

How do routers with equal standby-group find each other?

Shure, they have to be connected directly do each other, but in configuration you just configure for which interface the virtual router should exist.
4
votes
2answers
4k views

AODV sequence numbers and loop prevention

I am learning about the AODV (ad-hoc on-demand distance vector) protocol. I saw a "sequence number" with a value like "A 46"; however, I don't understand why incrementing this sequence number can ...
3
votes
2answers
336 views

Why R1 is not reachable to R3?

I didn't configure any routing protocol to any of the router and tried to apply static routes in order to get out of the network and I've configured static routing in a manner that if R1 sends a ping ...
3
votes
2answers
2k views

When is TFTP used? [closed]

It seems like a strange idea to transfer files using a connectionless protocol - so in what situation would you not care about if the entire file is delivered or not? I read somewhere that TFTP is ...
3
votes
1answer
91 views

Can't ping the management IP of Switch

My topology is: I am logged in to R1. I can ping 10.0.0.2 on R2 and 198.51.100.1 on R2, but can't ping the management IP of sw3 (198.51.100.2). What am I doing wrong? R1#sh ip arp Protocol Address ...
3
votes
1answer
4k views

How to erase running-configuration in Cisco IOS-XE?

I am using ASR 9k series Routers, which runs IOS-XE advancedmetroipaccess License I tried erasing NVRAM: and then tried to run copy start run But it gives me error : hostname#erase /all nvram: ...
3
votes
2answers
8k views

What is VLAN1 interface in routers?

Yesterday I had a look at my router configuration, and I saw that my office's local LAN gateway's IP address is written on the router's VLAN1 interface. What is a VLAN1 interface in a router? Is it ...
3
votes
1answer
1k views

Breaking broadcast domain through VLAN and Router

Why do we need to create VLANs to break a broadcast domain when the router can do the same? 1.Breaking broadcast domain through VLAN- Breaking broadcast domain through Router-
3
votes
1answer
590 views

Routing Between VLANs on Cisco 1921

I have setup a new VLAN for VoIP phones that are being installed. I would like to segment their traffic to Subnet 10.20.77.0/24. I added an IP address to the DHCP server of 10.20.77.11 to help serve ...