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.

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2answers
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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
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3answers
4k 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 ...
3
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1answer
577 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 ...
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3answers
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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 "...
12
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7answers
14k 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 ...
8
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1answer
5k 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 ...
1
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1answer
4k 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
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4answers
50k 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
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3answers
20k 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 ...
5
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1answer
890 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?
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2answers
253 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 ...
3
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1answer
1k 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
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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 ...
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2answers
157 views

Decrease the Router's buffer size

Through this topology, I want to decrease the buffer size of R2 in order to generate an ICMP Source Quench Message, but I have no idea how to do it. I'm open to other suggestions to generate a Source ...
22
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4answers
49k 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 ...
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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
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4answers
4k 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/ ...
9
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1answer
51k 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
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2answers
5k 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 ...
12
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3answers
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 ...
10
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2answers
4k 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 ...
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4answers
3k views

Advantage of layer 3 switch over Router

What is the advantage of Layer 3 switch over the Router ??
8
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3answers
3k 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 ...
8
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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 ...
6
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2answers
575 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. ...
2
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4answers
14k 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 ...
10
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4answers
17k 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
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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. ...
6
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3answers
2k views

How is NAT a hack?

Forgive me if this sounds a little amateurish, or if this is the wrong stackexchange, but...most of my entirely life I've had ipv4 behind a NAT router. I've been told that this was a hack; simply ...
5
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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
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3answers
25k 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
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1answer
907 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
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1answer
302 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
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1answer
62 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 ...
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1answer
41 views

Is there a way to determine my network transportation to specific path?

How can I determine my network transportation to specific path. I would like to determine that my data packages will go through specific routers.
12
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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
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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/...
6
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2answers
2k 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
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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 ...
6
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2answers
1k views

How does a router know the MTU of a network?

I've done several exercises where you're given the MTU of a net or subnet, but I wonder how routers know the MTU of the nets they're connected. I've learnt that in OSPF protocol this information is ...
5
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1answer
898 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
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4answers
11k 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
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1answer
185 views

What happens at the hardware level of a router when a packet is received and eventually triggers a process like ARP?

Please let me know where the gaps in my understanding are. There are many gaps, so please do not hesitate to fill them in or correct them. To my knowledge, what happens on the hardware level when ...
4
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7answers
632 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....
4
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4answers
687 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
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1answer
726 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
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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
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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 ...
4
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3answers
1k 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 ...
4
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3answers
1k 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 ...