Questions tagged [cisco]

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11
votes
2answers
12k views

In IPsec VPN, how is the pre-shared key encrypted?

I was doing IPsec VPN on ASA 8.0, and I understand a little about that. The initiator starts by sending its ISAKMP policy to the responder, and the responder sends back the matched policy. After that, ...
7
votes
2answers
1k views

NAT Overlapping

I am trying to do some networking lab. Basically, I have a network like this: So, is it possible to configure NAT router in such way, that PC1 and PC2 can access remote HOST and each other. The ...
8
votes
3answers
6k views

Implementing Cisco QoS model to end users

I have implemented the 4-Class QoS Model as described in this earlier post from 2013. This Core configuration is implemented on a Cisco VSS 6509-E setup running software version: Cisco IOS Software, ...
33
votes
1answer
70k views

Using SNMP to retrieve the ARP and mac-address tables from a switch

I would like to get ARP tables from a switch to a syslog-ng server that has been set up on Ubuntu Server 12.04 LTS. I have read about SNMP and I know the server will act as a manager and the switch as ...
19
votes
7answers
11k views

Best practice for the combination of HSRP and ECMP

The combination of ECMP (or other causes of asymmetric paths) and HSRP is broken by default in Cisco IOS; the default behaviour with this design floods unicast traffic excessively. What is the best-...
10
votes
2answers
3k views

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 ...
48
votes
24answers
94k views

How can I see which switchports are not in use?

On a large Cisco Catalyst switch stack, almost all switchports are patched. I need to identify the ports, which are not in use, for connecting further devices. Following switchports, cabling, patch ...
17
votes
4answers
68k views

Confusing A, B, C network classes

I'm studying IPv4 addresses and came across this whole thing about classful addressing. I get the idea behind it, bit there is something I find confusing: There are two "ABC" ranges: First one: A: ...
25
votes
4answers
107k views

How can I capture traffic on Cisco IOS switches?

For investigating a problem in client to server communication, I need to capture packets for analysis. However it's not allowed to install a packet analyzer, such as Wireshark or tcpdump, on client or ...
19
votes
4answers
24k views

LAP ignores DHCP Option 43 and uses CAPWAP UDP broadcasts

Background I am trying to redeploy Cisco 1242 LAPs on new Cat4507R+E switches, which means the IP address of the WLC is changing for that LAP. For some reason, I have to configure ip helper-addresses ...
10
votes
3answers
7k views

How are Weighted Fair Queuing and Weighted Random Early Detection related?

I'm trying to understand how QoS systems work and I'm not sure how exactly would WFQ and WRED interact. At first, I thought that WFQ is a queuing mechanism and that WRED is a congestion avoidance ...
15
votes
3answers
6k views

Configure Cisco ASA in Transparent mode: Layer2 DMZ w/ Vlan translation

I am in the middle of a project to migrate some existing switched ethernet dot1q trunks behind an ASA firewall... these trunks have five vlans each (numbered 51 - 55). This is a simple drawing of the ...
12
votes
1answer
4k views

Mac / CAM entries from non-Cisco switches with Q-BRIDGE-MIB

How do I do community string Indexing for other switches like D link DES 3526 and Brocade Fastiron SX800? I am running a java program to poll a specific vlan on a Brocade sx 800 l3 switch. The ...
17
votes
3answers
68k views

Is the “default VLAN” simply the default native (untagged) VLAN on all interfaces that have no configuration?

... or does the "default VLAN" have some wider meaning? Also, can it / should it be changed? For instance, if a switch is going into part of a network that is only one VLAN and it's not VLAN 1, is ...
8
votes
1answer
2k views

Staging Many Lightweight Cisco AP's for Deployment

My organization is soon going to be deploying approximately 600 new Cisco 2602i access points in a CAPWAP deployment with several 5508 controllers. This is an infrastructure refresh; currently we ...
12
votes
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 ...
10
votes
3answers
4k views

Inbound BGP load-balancing from same ISP router

I have two BGP routers for DIA with an issue with one provider in that the two links to this provider land on the same SP router. My ethernet handoffs via two separate MetroE links from another ...
1
vote
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
votes
4answers
49k 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 ...
15
votes
4answers
38k views

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-...
13
votes
2answers
28k views

Open a range of TCP ports in Cisco IOS NAT

ip nat inside source static 192.168.1.10 10.10.10.9 route-map RANGE ! route-map RANGE permit 100 match ip address 102 ! access-list 102 permit tcp host 192.168.1.10 range 3000 3389 any The ...
9
votes
3answers
19k 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 ...
6
votes
1answer
3k views

Cisco 867 forward UDP port range

I need to forward an UDP port range to a specific private IP address in my LAN. In order to forward one port to an internal IP I do: access-list <acc_list_number> permit <port_type> any ...
2
votes
1answer
487 views

Cisco Prefix List Won't Appear in Route Table

I have the following prefix-list configured on our router: ip prefix-list adsvr seq 5 permit 172.30.5.241/32 ip prefix-list adsvr seq 10 permit 134.239.130.143/32 ip prefix-list adsvr seq 15 permit ...
1
vote
2answers
128 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 ...
18
votes
5answers
88k views

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? ...
13
votes
1answer
13k views

What is the 5 level QoS model (through config example)?

I have heard people stating that their network "operates a 5 level (or layer) QoS model" Sometimes they also mention a 7 level QoS model. Can anyone provide me with a Cisco IOS config example of ...
21
votes
7answers
35k views

Difference between access list and prefix list?

Can someone explain with an example whats the difference between an access list and prefix list.
13
votes
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 ...
11
votes
3answers
6k views

What are the alternatives to OTV for stretching a layer 2 network across 2 datacenters?

We want to find a "safe" way to stretch layer 2 network across 2 data-centers, and since we don't have any equipment running NX-OS on either data-centers we can't use OTV. So what are the alternatives ...
10
votes
1answer
82k views

What does TCP DUP ACK mean?

In Wireshark, I see TCP duplicate ACK packets sent from the receiver to the sender. What does it mean? Does it imply packet loss? Thank you
9
votes
3answers
1k views

VM on a client connected to a Cisco 1262 unable to DHCP (but IPv6 works fine)

I recently replaced wireless at a site from the internal AP on an 877-WM with a (standalone) 1262 running 15.2(2)JB. I've configured the AP pretty much the same as I always do for Cisco AP's for ...
9
votes
3answers
19k views

Whats's the function of a loopback interface in routing protocols?

So I've got this task where I have to setup a virtual network with an OSPF routing protocol. I firstly ignored this loopback interface I had to configure on the routers since it didn't do any ...
9
votes
3answers
6k views

Generate list of subnets on switch using SNMP?

Is anyone familiar with an approach to generate a list of subnets on a particular switch (let's pick a more popular one - Cisco) using SNMP? How about a list of VLANs? If so, can you point me to the ...
30
votes
3answers
10k views

What is “oversubscription” in Networking?

I have a question about oversubscription in networking. I read a lot of documentation but I still don't understand what it means. I read the following on the Cisco website, oversubscription of the ...
19
votes
5answers
18k views

Should portfast be used on a port potentially connecting to an unmanaged switch?

I understand the basics of how spanning tree works and why you would want to use portfast on user access ports. When dealing with a topology with a large number of dumb switches under desks and ...
12
votes
1answer
6k views

Translating SNMPWALK output into human-readable format

I am asking this question which is related to a question I previously asked and was comprehensively answered by @MikePennington. When I asked that question, I intended to know how to poll arp table ...
10
votes
4answers
30k views

converting AP from CAPWAP to autonomous - BVI1 interface gets reverted back to DHCP

Has anyone ever gotten this message in the middle of converting a CAPWAP access point from CAPWAP to autonomous? *Mar 1 00:47:59.399: %CAPWAP-3-STATIC_TO_DHCP_IP: Could not discover WLC using static ...
23
votes
8answers
53k views

How can I force VTP clients to update their VLAN database from the VTP server, on Cisco devices?

I was doing some cisco exercises on configuring a vtp server and client, something I can't figure out is : I setup a vtp server, added my VLAN's I then took another switch that was attached to this ...
19
votes
3answers
7k views

What factors drive a Cisco IOS upgrade?

In order of preference/priority, what factors do you consider in driving an upgrade (or downgrade) with Cisco IOS? If no compelling factors exist, how long would you allow a particular version of IOS ...
13
votes
3answers
5k views

Management network. Best practises: big VLAN or routed interfaces

We are going to deploy a campus network with approximately 50 switches (Core, Agg, Access). Some of them will be L2 (20), and others will be L3 (30). We are thinking about how to manage these devices: ...
10
votes
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/ ...
6
votes
1answer
11k views

How do you configure a TACACS+ tac_plus server on Ubuntu 16.04 that authenticates against Microsoft Active Directory?

How do you configure a TACACS+ tac_plus server on Ubuntu 16.04 that authenticates against Microsoft Active Directory?
4
votes
3answers
3k views

Telnet - “Destination unreachable” response

I'm looking to implement, what I feel, is Telnet security when it comes to unwanted hosts initiating a Telnet connection to one of my devices. I can lock down a specific subnet or only allow a range ...
14
votes
3answers
43k views

How to Monitor Vlan Traffic?

We have migrated to a new ISP who provide us several services (Internet+VoIP+VoD) and have divided each service in one vlan 100,101,102 respectively. Now I'm looking for a solution to monitor each ...
11
votes
2answers
1k views

How did I break (half of) my network?

I'm looking for some post-event advice so this event doesn't happen again. We have a network core of two Cisco 4500x switches, configured for VSS redundancy. From those, we have iSCSI devices, our ...
11
votes
11answers
4k views

Locate a host on Network

What is the best method of locating a particular workstation on a VLAN ? I sometimes need to do this, if a workstation IP address, shows up on an ACL Deny torrent use High bandwidth usage (Top ...
10
votes
4answers
151k views

What can cause “FastEthernet is up, line protocol is down” on a Cisco Switch?

I wonder what can cause the first line output of the command show interfaces to be: FastEthernet is up, line protocol is down. In other words, Is the cable that is connected to the local interface, ...
8
votes
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 ...
7
votes
5answers
21k views

Copy running config in one line

I want to make a script to copy the running config of a switch 4506 in one line. So far, I see two option : copy run tftp: sw#copy run tftp://10.0.0.1/cfg.cfg Address or name of remote host [10....