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1500 questions
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3 answers

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 them to change in case I have to swap in a new…
J. L. Tympanum
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5 answers

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 can have a single autonomous system running EIGRP,…
Artur
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16
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5 answers

Do I need to set the enable secret on Cisco device?

I'm setting up a Cisco 2901 router. I have a login password on the console line, and the vty lines are configured to only accept ssh connections with public key authentication. The auxiliary line is shut down. There are only two admins who will be…
Marwan
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16
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4 answers

What happens when 2 computers transmits at the same time to a 3rd one in a full duplex switch?

Consider the following scenario: I have 2 PC's (PC1 and PC2) that wants to transmit at the same time to PC3 in a full duplex ethernet switch. Let's consider that all ports are in the same VLAN, so what happens internally in the switch? Who transmits…
Juan Jose Polanco Arias
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16
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4 answers

Why does this router fail to use multiple, equal-cost routes from OSPF?

A Brocade router running NetIron 5.2, and a Dynamips emulation running IOS 12.4 both fail to dependably use equal cost paths in what seems to be a very simple configuration. I say "dependably" because I did observe very briefly the expected behavior…
neirbowj
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16
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2 answers

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 think I'm hardly sending much traffic outbound on…
generalnetworkerror
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16
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3 answers

How is the root bridge elected in STP?

How does STP/RSTP determine which bridge is the root bridge, and how are paths to the root bridge selected?
nos
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16
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6 answers

Use BGP to defend against a DDoS attack originating from remote AS

I have a question regarding BGP and how to achieve this configuration. My enterprise core router is connected to an ISP (single homed). This router has already exchanged the specific public ip prefixes to the ISP in BGP updates. Now lets says there…
Harish Reddy
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15
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4 answers

How are two "ip helper-address" statements handled?

I've discovered a subnet with two "ip helper-address" statements. This is not our normal configuration. interface Vlan300 ip address 10.1.3.2 255.255.255.0 ip helper-address 10.2.1.10 ip helper-address 10.3.1.10 Looking at our DHCP servers, it…
Pseudocyber
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15
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5 answers

Should i run UDLD with spanning tree?

Can spanning tree and UDLD be run together, and if so, is this a good idea?
Aaron
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15
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8 answers

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 which are provided via cross connects to other…
Kranar
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15
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5 answers

How exactly does an Ethernet collision happen in the cable, since nodes use different circuits for Tx and Rx?

I am trying to understand how a collision occurs in Ethernet, especially when a duplex mismatch exists or when on a legacy Ethernet network two nodes transmit simultaneously. Everyone explains the collision in an upper level (two frames collide…
Christos Dalamagkas
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15
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3 answers

Serialization and serialization times in 40G/10G and 100G/25G Ethernet

I've recently been involved in discussions about lowest-latency requirements for a Leaf/Spine (or CLOS) network to host an OpenStack platform. System architects are striving for the lowest possible RTT for their transactions (block storage and…
Marc 'netztier' Luethi
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15
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5 answers

Do Wi-Fi and IEEE 802.11 mean the same thing?

I would like to know if Wi-Fi can be generally referred to as the IEEE 802.11 standard or if the latter is a more general family.
Abdulhameed
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15
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6 answers

Time to switch to IPv6?

I am thinking of upgrading our networking situation and am considering a migration of IPv4 to IPv6. Is it too soon to be considering this move as it looks like much of the networking gear and OSen are ready for it? Where do I lose out in such a…
mdpc
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