Questions tagged [cisco]
The major provider of networking equipment. This is a generic tag to be used when no more specific tags are available. See the list of tags in Help Center Tag page.
176
questions
7
votes
2
answers
2k
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 ...
- 173
11
votes
2
answers
16k
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, ...
- 153
9
votes
3
answers
8k
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, ...
user36472
33
votes
1
answer
88k
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 ...
- 685
18
votes
7
answers
13k
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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-...
- 29.8k
9
votes
3
answers
28k
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 ...
- 193
3
votes
1
answer
346
views
Upgrading Cisco 819 to 809, can I connect devices to 2 routed ports and be on same subnet?
The company I work for has multiple remote "IoT" style sites connected back to the datacenter via a Cisco 819 cellular router. We are in the process of upgrading these to the newer Cisco IR809 routers ...
- 33
48
votes
24
answers
103k
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 ...
- 3,374
35
votes
3
answers
26k
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 ...
- 3,098
27
votes
4
answers
114k
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 ...
- 3,374
19
votes
3
answers
86k
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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 ...
- 353
18
votes
4
answers
25k
views
Cisco APs ignore DHCP Option 43 and use CAPWAP UDP broadcasts
Background
I am trying to redeploy Cisco 1242 LWAPs on new Cat4507R+E switches, which means the IP address of the WLC is changing for that LWAP. For some reason, I have to configure ip helper-...
- 29.8k
17
votes
4
answers
72k
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: ...
- 671
15
votes
3
answers
7k
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 ...
- 29.8k
12
votes
1
answer
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 ...
10
votes
3
answers
8k
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 ...
- 685
10
votes
2
answers
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 ...
- 14.9k
50
votes
6
answers
111k
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 ...
- 1,010
19
votes
4
answers
73k
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 ...
- 963
15
votes
4
answers
45k
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-...
- 887
14
votes
3
answers
50k
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 ...
- 2,008
13
votes
2
answers
30k
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 ...
- 131
12
votes
7
answers
16k
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 ...
- 3,129
11
votes
2
answers
2k
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 ...
- 243
10
votes
3
answers
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 ...
- 7,094
9
votes
1
answer
7k
views
Static routes: numerical next-hop vs interface
I'm reviewing old Cisco modules, and in CCNA 2, Module 2.5.1.2, it states,
Under certain conditions, the network administrator will not want to configure the static route with an exit interface but ...
user3046
8
votes
1
answer
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 ...
- 8,288
7
votes
1
answer
3k
views
BGP authentication-key-chain vs. authentication-key
I found a neat little behavior on a Juniper box I was working with today.
We were migrating from a Cisco ASR to an MX and all of our internet exchange peers that had authentication configured didn't ...
- 7,044
6
votes
1
answer
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 ...
- 206
5
votes
3
answers
2k
views
Traceroute doesn't show one hop?
I have an interesting issue where my traceroute skips one hop on the way. I do not know why but it seems to be some kind of Juniper behaviour which I do not understand yet. Blue routers are Cisco ...
- 141
4
votes
3
answers
1k
views
Collision domain question
I'm studying for my CCENT exam, and not quite sure why the book (official Cisco) says that there are 5 collision domains in this example. Isn't it supposed to be 4? The hub on the left, the hub in the ...
4
votes
3
answers
14k
views
Cisco 3725: Why default-gateway does not appear on `show ip route`
My network topology is as follows
From R1, I was not able to ping R3.
Packet capture on R3 shows that echo request received, but no reply from R3.
It turns out that default gateway did not appear ...
- 311
3
votes
1
answer
608
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 ...
- 213
1
vote
2
answers
384
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 ...
1
vote
1
answer
6k
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
...
- 4,371
1
vote
1
answer
739
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 ...
- 121
0
votes
1
answer
665
views
CISCO PACKET TRACER "INVALID IP ADDRESS"
Hi I am still new and studying about networks have here 234.1.18.6/29 address and mask but when I try it out on Packet tracer it gets me an invalid message. I cannot understand why this address are ...
- 11
24
votes
8
answers
68k
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 ...
- 4,161
23
votes
7
answers
40k
views
Difference between access list and prefix list?
Can someone explain with an example whats the difference between an access list and prefix list.
- 545
21
votes
3
answers
4k
views
CEF operations on L3 switch vs router
I understand that L3 switches use CEF for faster packet forwarding. However, CEF will not work for packets that need to undergo NAT. Does this mean CEF isn't used by edge routers and edge L3 switches? ...
- 1,005
19
votes
5
answers
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 ...
- 688
19
votes
3
answers
9k
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 ...
- 7,094
18
votes
1
answer
145k
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
- 303
18
votes
4
answers
9k
views
Are there any reasons to not use BFD?
In looking to implement Bidirectional Forwarding Detection (BFD) it seems to be very flexible in terms of timer tuning, light weight regarding any overhead and it's flexibility in terms of overall ...
- 2,087
16
votes
5
answers
93k
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? ...
- 369
13
votes
5
answers
15k
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 ...
- 3,310
13
votes
1
answer
33k
views
RIB vs FIB differences?
Can someone explain the differences between a RIB and FIB a little further? I didn't see any similar questions on the site so I thought this would be a good addition. The RIB routes and the FIB ...
- 1,010
13
votes
6
answers
344k
views
Finding Non-Cisco End Device IP Addresses Connected to Cisco Switch
I have Cisco catalyst switch, with many VLANs and address ranges.
How do I find IP addresses connected to the switch that are not Cisco devices?
- 812
13
votes
3
answers
37k
views
Mac-flap due to roaming clients on wireless
We are running an Aerohove wireless network (controller-less).. I occasionally get mac-flaps within the VLAN tied to a SSID. I know this is coming from a roaming client.. The problem is that the ...
- 894
13
votes
1
answer
15k
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 ...
- 5,290