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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6
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4answers
13k views

When/Why to use OSPF?

This question has been hanging around in my head for a while; all the way from back in 2012, when we replaced our core network switch. This switch was actually a stacked pair of old 3Com 4900sx, and ...
4
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1answer
110 views

BGP | Advertise a summary prefix out to customer location

I don't know what I should be using for this or how I should go about it. In my lab where I am testing out the BGP configs that I've learned I want my ISP topology to have a summary prefix for the ...
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2answers
4k views

What's the DF flag mean in IP packet header?

In the IP package, there is DF flag: Don't Fragment. I have doubt about it, is it mean let all the L3 device do not to fragment the IP packet (if the L3 device found it is bigger than MTU, device ...
3
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3answers
154 views

How is traffic forwarded though IXPs if route servers do not forward any traffic

while i was studying about IXP route-servers, i read that they do not forward any traffic. I get that a route server is a "control plane" entity and it is used for easier bgp peering. However, i ...
3
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2answers
2k views

Strange router's MAC address from ICMP Echo Reply?

Using Wireshark to capture ICMP packets (Windows) using ping to google.com, I can see the source-MACAddr of the ICMP Echo replies is not the same as the MAC address of my direct router (which is the ...
5
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3answers
17k views

Why does iBGP require a full-mesh?

I understand that routes learnt via iBGP can't be redistributed to other iBGP peers to avoid loops, but then why is a iBGP connection between two routers that don't have eBGP connections needed? They ...
1
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1answer
565 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 ...
3
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1answer
305 views

ARP Router issue

I have a question when a Router receives ARP request to a host that dosen't exists on the forwarding table for that router does the. And this Router is not the next hop either will the Router continue ...
9
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3answers
19k 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 ...
8
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1answer
1k views

Dealing with IP Spoofing

Border routers, which are routers that span two or more sub networks, can be configured to block packets from outside their administrative domain that have source addresses from inside that domain....
10
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3answers
1k views

Does anycast addressing add additional latency in any way?

Does anycast addressing, in itself, add any additional latency to network connections? Specifically, if you had two servers located in the same data center that had extremely similar routes/number of ...
0
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2answers
260 views

What are the differences between packet forwarding and network address translation in layer 3?

What are the differences between packet forwarding and network address translation in layer 3? Is packet forwarding done by a router between two networks that use public IP addresses? Is network ...
1
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1answer
38 views

Where can one find how much memory is currently allocated to logbuffer?

Do you know where it can be checked, how much memory is currently being used by the logbuffer? some-switch#show log | i Buffer|Trap|udp Buffer logging: level debugging, 2268 messages logged, xml ...
10
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2answers
46k views

Cannot use 5GHz band Wi-Fi from channels 100-140

My AP operates in the 5Ghz band. There are no problems using Channel 36 to 64; however, clients can't even detect the SSID if I use Channel 100 to 140. Below is a screenshot of Netspot showing all ...
3
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3answers
3k views

How to enable DHCP Cisco router

This is what I have done in my GNS3 R3 - Router R4 - Switch I have installed GNS3 and trying to enable on Router as mentioned above depict. How to enabled DHCP on Cisco router R3 ?
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3answers
284 views

Using 2 different ISP In case one dies

It's my first ever post in here and I hope not the last. I'm looking for some advice. I'm trying to reduce my internet downtime for a local network. My setup. Mix and match computer environment (...
0
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1answer
155 views

Cisco ip helper-address

I am looking at the DHCP documentation and i cannot seam to find how to configure the router to use a loopback interface as the relay-agent. My objective is to use option 82 so that the dhcp server is ...
0
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1answer
104 views

Is it possible to assign an IP to a tagged dual-mode port (Brocade)

I have a router (ubiquity USG) and a Brocade FCX648 Layer 3 switch. (I have a second one in a stack, but that's unrelated). The end goal is to be able to connect the switch to my router, provide IPs ...
6
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2answers
1k views

Undo last command(s) in case of losing connection to a Cisco Router

I would like to configure an interface on a remote Cisco router (ISR 4000 series) with IPsec. The only way to connect to it is through the interface that I am trying to encrypt. I want to ensure that ...
5
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2answers
17k views

pfSense 2.3 How to setup each Lan traffic goes only over specific gateway

I am running a pfSense 2.3 box with 4 NICs. Now i have 2 different ISPs (one Cable & one DSL). How Can i configure, that all traffic from LAN1 goes ONLY over WAN1, and all traffic from LAN2 goes ...
0
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1answer
87 views

Who initiates PPP Keepalives after PPPoE session is Established between Modem and BNG?

Hello Everyone, In case of DSL Modem , normally service providers employ PPPoE connection between Modem and BRAS (BNG). We all know that when Modem dials , it goes through PPPoE stages namely 1 ) PADI ...
1
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3answers
102 views

Combining NAT an tunneling

I was reading a text and a doubt came to mind. Suppose there is an interface in a router that implements NAT. That same interface is the extreme of a tunnel. If I was to send a message through said ...
1
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3answers
99 views

One client: static IP vs Static lease DHCP vs. DHCP limited range to 1 slot

I want to attach one client (only 1 maximum) to network router ethernet port. I want to always know the client's IP address, for my port forwarding settings. Using DHCP with range the client IP could ...
0
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1answer
79 views

BGP unnumbered on P2MP link

I'm wondering what will happen if BGP unnumbered session is configured on a link that has multiple routers on the other side which are both IPv6-capable and will both reply on RS and produce RA ...
1
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1answer
521 views

Factory reset Cisco N520-4G4Z-A

I'm having some issues doing a factory reset on above mentioned Cisco box. I've tried several different key combinations and unfortunately previous owner does not remember password The examples on ...
1
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0answers
44 views

Mistakenly added switch configuration on Cisco router 2951 so now it is showing gibberish data on CLI

I have Cisco 2951 router in which my colleague mistakenly uploaded switch configuration from tftp server. Now it is showing gibberish data on CLI when it boots up. I tried to get into the ROMmon mode ...
1
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2answers
78 views

How does an L3 Supported Switch differentiate L2/L3 Packets?

I had a managed or layer 3 supported switch (it can process both layer 2 and layer 3 packets). Now a packet from a connected host comes to it, sending traffic. How does the switch decide to process it ...
1
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1answer
135 views

GNS3 can not ping from ethernet interface to serial interface

So I am doing a Lab for one of my classes involving ipv6 and routing using EIGRP. When I set-up the network and assign the router interfaces with IPV6 address I get an issue pinging the whole network. ...
1
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2answers
65 views

Is there a way to know the length of the cable used between the connected SFPs on a switching/routing device?

I have connected two Juniper routers with a QSFP28 optics and I need to find out the length of the optical cable I have used. Is there a command to check that in the router?
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0answers
12 views

Does the control packets flow into a router/switch through forwarding plane? [duplicate]

I know there are two platforms in any networking device separating the control packets from the traffic, which I call control plane and data plane. My question is, how does the control packets enter ...
2
votes
2answers
825 views

How to block advertisement of a prefixes recieved from 1 BGP neighbor to another

I have a eBGP topology as follows: RTR1 ------ DUT ------ RTR2 (AS100) (AS200) (AS300) I do not want any routes sent by RTR1 to be advertised into RTR2 by DUT I do not know what exactly the ...
0
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0answers
25 views

Switch vs. Router and sequence of OSI Model [duplicate]

As I understand it: A switch (layer 2) seems to define a LAN and a router (layer 3) enables communication between distant LANs. A device on a LAN will give it's MAC address to the switch upon ...
1
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3answers
254 views

Why is in all arp table snmp oids an interface index before the ip number?

When I want to get arp information about a single ip number or subnet, I have to snmpwalk the whole arp table, as some oid architects had the "great" idea to always insert an interface index ...
1
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2answers
808 views

Safe to remove ip default-gateway?

We recently changed IP schemes from 192.168.x.x to 10.x.x.x In doing so, I noticed that the prior network engineer had ip default-gateway in the configuration pointing to an old default gateway that ...
0
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2answers
673 views

I'm confused about ethernet interfaces (eth/in, eth/out, eth/local)

I'm using an Edgemax router (EdgeOs), and even after having read posts and checked internet pages, I'm still very confused about which of my ethernet interfaces are communicating with what. My LAN is ...
0
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2answers
145 views

Loopback interface

I have a theoretical question about the loopback implementation on a router. I understand that the idea of a loopback interface is that it is a virtual interface which never goes down due to a ...
-1
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1answer
56 views

EdgeRouterX not routing traffic [closed]

New to this. I have a tc4400 modem which works fine: when connected straight to my computer, internet passes. However when I connect my EdgeRouterX to the modem and ssh into the router, pinging any ...
1
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0answers
25 views

Can I use a wireless access point (or two) to extend my existing wireless network? [closed]

In large commercial buildings I typically see several ceiling mounted Wireless Access Points. When moving throughout the building, I do not have to continually reconnect to different networks (or ...
1
vote
1answer
104 views

How does router know MAC addresses of computers that are connected to a separate switch? [duplicate]

i am a newbie but i need to understand this ARP thing. In my company we have a router that has 3 switches connected to it. On the switches there are more than 100 hosts. I know that switch learns and ...
3
votes
1answer
316 views

Is this a valid OSPF topology?

In the following topology: every Backbone router is an ABR. Router 2 belongs to three different areas, area 0, area 1, and area 4. is this a valid topology for OSPF ? it works as expected and it ...
1
vote
2answers
104 views

Routing Protocols and sharing information

I am running multiple Protocols on different Routers as so: R1-RIPv2 EIGRP OSPF R2-OSPF and RIPv2 R3-RIPv2 and EIGRP R4-EIGRP and OSPF This is not a practical exercise, it is just to explore how ...
1
vote
1answer
118 views

Do all devices which use Wi-Fi (802.11) use CSMA/CA?

I know this is quite trivial, but I just want to know if all devices which support Wi-Fi through interface cards/hardware (like laptops/PCs/phones..etc) use CSMA/CA irrespective of their router/...
7
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3answers
8k views

How does a router learn about networks that can be reached from its interfaces?

I was studying, and I got stuck in trying to find out the best way to answer this question: explain how a router learns about networks that can be reached from its interfaces and how it routes ...
0
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1answer
42 views

Routers FastEthernet interface clock autonegotiation protocol

In routers, for serial interfaces, we need to manually set the clock at the DCE router so that the ends of the connection can communicate. I know that in this way we are using time-division ...
1
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2answers
132 views

Using WAN IP for a host instead

I have a single static public IPv4 address from my ISP. So I understand that i can just forward all traffic using port forwarding to one of my private IPs, but still I am wondering if this is the ...
43
votes
6answers
98k views

Difference between control plane, data plane and management plane?

I think I understand these concepts, but I'm a little rusty. Can someone give a concise, easy-to-understand explanation of these concepts? The planes are logical concepts, aren't they? Is this a Cisco ...
0
votes
1answer
38 views

allow 2 machines to communciate each with their own network? [closed]

2 networks. Network 1 local and i want to be able to receive and send information to network 2 which is at a remote site, branch site. How do i go about connecting both networks so that both machines ...
0
votes
1answer
126 views

Suspect MTR showing incorrect packet loss through router; other tools are not showing loss

Using MTR (sending TCP with or without SYN), I'm consistently seeing packet loss on one intermediate router in the path. UDP does the same. I'm use TCP to avoid the ICMP packet flood limits set. I ...
1
vote
3answers
656 views

Routing between completely separate private networks

I’ve got a request from a partner vendor in a completely separate routing domain to directly route a /24 rfc1918 network on my rfc1918 internal network. The proposed solution has their handoff ...
6
votes
6answers
19k views

Best practice - Set static IP in device or router?

Pretty simple question. What is the industry best practice? In a small business which has computers which require static IP addresses is it better to set static IP addresses for devices on the ...

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