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1500 questions
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4 answers

Best practice using Cisco's "ip-helper" for DHCP?

Our topology is such that we have two 4510's in our IDF closets. Each switch has a data VLAN and a voice VLAN. The switches are layer 2 trunked to the core, where the VLAN interfaces are, routing happens, and DHCP is forwarded to the DHCP…
Pseudocyber
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16
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3 answers

What does logging synchronous command do?

Can somebody describe me what does logging synchronous command do ?
Abiral
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16
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2 answers

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, the AS_PATH only needs to be of the same length.…
sdaffa23fdsf
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16
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5 answers

Is PoE compatible with Gigabit Ethernet?

I'm looking for specifications for Gigabit Ethernet in connection with PoE. I saw somewhere that 1000BASE-T uses all 8 lines of the twisted pair cable. If that is the case, how does it work with PoE?
Pedr0
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16
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5 answers

About the switchport mode

I am new to network Engineering. I find it is hard to distinguish and understand different switchport settings. Why can I have a switchport set to access, auto, or dynamic? What are they used for? Are those functions only used for a host to switch…
Samuel
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16
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5 answers

What causes total output drops on a cisco switch interface?

I have an HP c7000 blade chassis which contains Cisco 3120X and Cisco 3120G switches running ios 12.2(58)SE1. The blades themselves are very lightly loaded yet many interfaces on different blade switches in the chassis show a fairly high number of…
User123456
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16
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3 answers

What is the purpose of TIME WAIT in TCP connection tear down?

I found that the reason the active closer enters TIME WAIT is to make sure that the final ACK is not lost. But how does it know if the final ACK is lost? Will the passive closer resend the FIN and then the active closer knows the ACK was lost? Here…
czhao
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16
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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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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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