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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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 ...
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What are the benefits and cons of IGMP snooping?
Our new router is asking if we want IGMP snooping enabled. Not being familiar with this, I looked to the internet and got the following wiki description:
IGMP snooping is the process of listening ...
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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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What stops someone from configuring their network with IP addresses they do not own?
Here's the scenario. I was picturing a university that bought a range of IP addresses. I think their network would still be connected to an ISP (right?), but they'd have freedom to configure stuff the ...
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Difference between router and gateway
What is the exact difference between router and gateway? In Network configuration we set the default gateway IP address, but in reality we call the device configured with that IP address as router?
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Building new network and need 200+ wireless devices
I'm planning the network for my company's new office space. I'm not an expert so I'd like to present my plan and ask y'all nice folk to tell me if and where I'm making mistakes.
Assumptions:
Office ...
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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 ...
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Cause of high CPU load on Juniper peering router's routing engine
Recently the routing engine CPU utilization on two of our Juniper peering routers increased from ~10-20% average load to 80+%. I'm trying to figure out what's causing this (and how to get this high ...
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Cisco command to show which interfaces an ACL is applied to
For Cisco routers and switches, is there a show command, or something similar, that will display what physical and logical interfaces an ACL is implemented on and what direction it is applied in?
I ...
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Is it possible to specify a route for a packet to take?
So, AFAIK, packets "hop" between routers. Packets are forwarded via a router's default path until it gets to destination IP. So is it possible to specify a specific set of routers this packet "hops" ...
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Why would a switch be connected to a router using three ethernet cables?
In our rented office, we have a router (BT smart hub) connected to a large switch (model unknown). The two are connected using three ethernet cables, thus:
-----------------------
| 1 2 3 4 ...
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Automate configuration backup (every minute) in Cisco IOS
I'd like to make my Cisco router automatically do a copy run TFTP (and populate the fields automatically) every 1 minute. I'd also like it to be run in the background. Anyone know if this is possible/...
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Backing up Cisco router configuration - including ssh keys
We have some Cisco 2821, 2921 and 1921 routers in our shop. I can back up and restore the configurations by copying out or in the startup-config file, but what about the keys for ssh? I don't want ...
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Output Drops on Serial interface: Better queueing or Output queue size?
On Internet edge routers speaking eBGP to multiple carriers and iBGP to one another, all interfaces on the LAN and WAN side are GE except for one Serial full-DS3 (~45Mbps) on each router. Although I ...
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BGP multipath with different ASNs feasible for production networks?
on Cisco (this command is hidden for some reason)
#bgp bestpath as-path multipath-relax
The default BGP behavior only installs only routes with exact the same AS_PATH into RIB. With multipath-relax, ...
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class-default matches control traffic?
I'm seeing an issue with BFD on a link that's being policed egress where it appears during times where the policer is maxed BFD packets are not getting to the other side. I'm wondering if BFD hellos ...
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How to connect 5 different networks together?
I have a network consisting of three servers in a data center, all of which are connected to each other via a switch.
In addition to this I need this network to access 4 additional networks, most of ...
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Why is my Router's WAN IP different from public IP? [closed]
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 ...
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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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What is SNR Margin and Line Attenuation?
I'm currently using an adsl connection and last week an engineer from my ISP came and told me that my SNR margin and line attenuation is not good, and they need to replace the main telephone cable to ...
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Should a router use SLAAC for IPv6 address assignment?
I am a little confused by the following 2 RFCs relating to IPv6:
RFC 4862 (IPv6 Stateless Address Autoconfiguration)
RFC 7084 (IPv6 CE Router Requirements)
RFC 4862 states:
The autoconfiguration ...
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BGP regular expression .+_.+_.+_.+_.+_.+_.+_.+_.+_.+_.+_.+
could anyone tell me what ip as-path access-list 100 deny .+_.+_.+_.+_.+_.+_.+_.+_.+_.+_.+_.+ stands for?!
I searched over the internet for the meaning of this regular expression, but I was unable to ...
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What happens when the ARP cache overflows?
In at least one implementation there is a hard limit on the capacity of the ARP table. What happens when the ARP cache is full and a packet is offered with a destination (or next-hop) that isn't ...
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Is the MTU of Ethernet still 1500 Bytes?
So basically do the modern routers in the internet still use 1500 as the MTU of Ethernet? or the 1500 Byte was for the old days?
What I'm asking here is what is the MTU of Ethernet in modern Networks?...
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What is the difference between a VRF and GRF? (cisco)
I've heard about VRF's and GRF's, but was is the difference between those 2? (cisco)
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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 ...
user33076
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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 ...
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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 ...
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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 ...
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Error: `EIGRP is restricted to stub configurations only on this platform`
We just bought some new Cat4507R+E distribution switches. When we bought the switches, we asked for an Advanced Services K9 image, but our reseller told us they only come with a Universal K9 image. ...
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What are the reasons for seeing an incomplete ARP?
As was mentioned in this post:
The reason for seeing an incomplete ARP is that "An ARP request was sent for that address, but the host with that address is not up and running on the LAN, so there is ...
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When does switch talk to router
I have read a lot on how switches forward within LAN, but little about how switch talks to router.
When does a switch send packet to router ? Is it when it does not find recipient on the same LAN ?
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Do today's routers prevent fake IP headers?
I know people can modify the IP headers and change source IP address, but it should be simple for network devices to detect those messages. If they don't, why is it so hard? Does it add too much ...
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RIP routing is broken between two routers
There are 2 routers connected something like this:
Network1 ----- (172.16.1.1/24) Router 1 (172.16.3.1/30) ------ (172.16.3.2/30) Router 2 ------ (172.16.2.1/24) Network 2
I try to add addresses for ...
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Using IP addresses from IP pool given by ISP
My ISP says that it can provide an optic fiber connection with a pool of 4 static IP addresses (subnet 255.255.255.248 i think).
My question is that if I get that connection,
1 ip will be used for ...
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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 "...
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Cisco IOS built-in SSH client default version
You issue the command ssh 192.168.97.97 from a IOS device and the destination IOS router/switch SSH server is accepting both SSH versions. Being that you did not specify a version to use on the SSH ...
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IPv6 Subnetting - Block RA on Switches?
I'm currently planning a v6 only small datacenter network.
Imagine for now one deployment consisting of 6 racks with 12 servers per rack.
Each server has 2 NICs for two physically separate networks (...
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How much RAM you actually need to keep whole global BGP routing table?
It seems that different sources claim very different RAM consumption for having whole BGP routing table information in RAM and having the router to correctly route the traffic.
According to ...
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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 ...
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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 ...
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Embedded routers vs. software routers in the datacentre
I've been looking for a new 'core' router to put in our new rack which is colo'd at a nearby datacentre. What I've come across is the usual Cisco/Juniper/Brocade lineup, with the usual unattractive ...
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Redundancy between router and servers
In the past, I was using a NetGear GS724T between my router and my servers. Unfortunatly the switch suddenly died.
Now I've changed it for a GS748T and also bought one more and I am wondering how I ...
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What is backpressure in the context of routers?
There are several references to backpressure as regards to the internal bandwidth and switching fabrics of routers and switches. What exactly does backpressure mean, and what are the real world ...
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If two NICs are bonded and connected to different switches how does a router decide which switch to forward the packets to?
I am trying to understand how the architecture works in case of NIC Bonding. The scenario is: There are 2 NICs on the same system. Both are bonded to support failover and load balancing. Hence the IP ...
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How does the computer detect the router?
Is the router always broadcasting "I'm here" (say, every period of time) and the computer listens or the router listens and once the computer broadcasts "is there a router here?" It responds?
It ...
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Long login delay when cisco device is booted
Whenever we boot or reboot a Cisco router or switch we have to wait a number of minutes before we can get a username prompt for login. We get a few fail messages
Press RETURN to get started.
% ...
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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/
...
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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 ...
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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 ...
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