Understanding NAT Table And Its Chains (pre-routing / Post-routing And Output)?
May 28, 2011
I'm learning about iptables, but I don't fully understand the chains of NAT table (prerouting, postrouting and output).I'm specially in doubt about prerouting and postrouting. As far as I know, DNAT can be made with prerouting and SNAT can be made with postrouting, so I think prerouting is for input and postrouting is for output, but the material I'm reading (and another sources) are not clear.
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Apr 16, 2012
I've been working on breaking down and understanding the default auto qos configuration on a Cisco 3750 in the hopes of putting together a QoS strategy that will fit our environment. I'm having some difficulty understanding how the "mls qos queue-set output" syntax works.
From another post, at [URL], the author offers the following example and explanation;
mls qos queue-set output <1/2> threshold 2 400 400 100 400thresshold 1: 400%
thresshold 2: 400%
thresshold 3: 100% (implicit, not configurable)
reserved: 100%
max: 400%
However, I'm having trouble understanding what is meant. Here, it looks like it's saying, for example;
mls qos queue-set output 1 threshold 2 400 400 100 400
How come there is syntax stating "threshold 2" when in the succeeding part the 400 refers to thresshold 1 and threshold 2 again? The syntax 400 400 is, apparently, already referring to thresshold 1 and 2, no?
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Jan 16, 2013
In datasheet of WS-SUP720-3B - link- was said that are only supported around 256K routes (fib?rib?).With this value I can't get 2 full bgp - that is around 850K ..
The supervisor is that control this or just memory ? I said this because I have a 7204-npe-g1 whith 2 fullrouting and 1G of and he are ok..
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Apr 23, 2013
I have a C2960-24TT-L Switch with the following problem:When the Power Cord is plugged in the Switch, all switch indicator LEDs go on very briefly. Then SYST LED blinks very briefly, goes on steady and remains at this state without any indication at the console.Tried the reset by holding the MODE button while plugging in power but I still get no indication at the console. All is fine with console, meaning that if I take out the cable and plug it in another switch, then I see all that there is there to be seen.My question: Is the switch beyond repair or is there something that can be done to get the switch to run POST and boot at rommon so that I can reload SW and configs?
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Jan 10, 2013
We've recently inherited a platform with little handover and also minimal networking experience.We're going 100 miles an hour in learning, but I'm a bit confused with the idea of a L2 switch with no IP assignments to ports, so using VLANs, and a L3 switch with IP assignments. And the combination of both.We have 2 Cisco 3750 switches, along with a whole host of other hardware, so we're starting at this "gateway" to start breaking things down.
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Nov 12, 2012
We have two Cisco 3560E layer 3 switches at the core of our network. The switches are configured as an HSRP pair and the clients on our network point to the HSRP address as their default gateway. So if CORE-A dies, then CORE-B will pick up the address and the default route for the clients will continue to be available.We also need to specify a few static routes on the core switch to allow us to get to specific networks. Is there a way to do this so that the routes failover in the same way that the default gateway does?
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Jan 31, 2012
I tried the "Advanced Routing" Feature over the RV-042 V3 Dual WAN VPN Router , And the New IP Subnet i added ( 10.0.7.0 ) in the Static Routing Table does NOT Appear in the Routing Table of the Router. Please review the attached Print Screen for both the Static Routing Entry Configuration & the Routing Table of the RV-042 Router.
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Dec 5, 2012
I started using RIPv2 on Packet Tracer. I got two subnets to connect with two routers. After I completed that, I decided to add a third router. How to setup the Routing Table for atleast R3 ?
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Oct 2, 2012
I am using Cisco 2911 & IOS version is 15.1. My problem is that after some days (e.g. 15-20 days), the routing table suddenly stops updating & then I have to enter the default route again to make it up. I am using Track 1 to track default route here. After primary link goes down, the Track is also going down but after coming the primary link up, the track is not coming up. So, I have to add the default route again to make it up.
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Nov 14, 2012
We have small which I'm looking to implement and have built this on GNS3.
We have:
Router A in site 1
Router B in site 2
Router C in site 3
Router A and B are connection via a point to point 100M link and from Router C we have a 2 point to point one of which is 5Mpbs and going to Router A and Router B.
For Router C to reach Router A network it will go via Router B and these are 100M connection. When the link between Router A and B goes down. Router C should update and start using the 5m route.
For some reson, the routes are not updating. I have to do 'clea ip eigrp ne' for the routes to update and if I reload the routers all works well, it seems the problem is intermittent.
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May 22, 2013
I am attempting to filter a specific host(s) from my OSPF routiing table on a ASA 5550 (ABR) using LSA prefix lists. However, when I look at the other routers in that area, I notice that ALL LSA type-3's are being removed (10 hosts are now missing from the routing table). I have verified the filter is working on the ABR, but I can't figure why ALL hosts/routes that were coming into the area are now being filtered instead of the specific one that I want to filter out.
Here is the config on the ABR:
prefix-list pdm_pl_000 seq 10 permit 206.253.180.137/32
!
!
router ospf 1
network 10.0.0.0 255.255.255.0 area 0
network 10.150.10.0 255.255.255.0 area 10
network 10.150.252.0 255.255.255.224 area 10
[code]....
The 206.253.180.137 host is actually coming from Area '3'. Am I doing something that is removing all type-3 LSA's?
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Jun 5, 2012
I have a Cisco CBS3020-HPQ chassis switch running IOS 12.2.(25r)SEF3. One of the ports is in "disabled" state but when I try to unshut it, it doesn't work, the switch logs shows the following event:
%PLATFORM_ENV-3-LOOPBACK_PORT_POST_ERR: Gi0/1 can't be brought up because it failed POST in Loopback test
how do I resolve this, the port is unusable since I can not get it out "disabled" state.
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May 14, 2013
I pulled a brand new Cisco 3850 Switch out of the box yesterday. Following the Quick Start Guide, I put in the power module, powered it on, and waited for it to complete POST. Then, I plugged in an Ethernet cable between a laptop and the switch on a port in the front, and went to the web interface at https://10.0.0.1. I got to the Express Setup, and attempted to change the IP address of the switch to an IP on my LAN, along with other options. When clicking submit, it didn't appear to take. Upon refreshing in the Express Setup, the IP config was blank, so I once again configured it. This time clicking submit brought up a message that it was changing the IP address. I waited for it to finish, and when it looked done, I powered the switch off and took it to a different room to hook it up to the LAN for further configuration.
When plugging in the power at that point, the switch starts through the normal light process (System LED blinks green slowly), and then eventually the System LED blinks green very fast and never stops. It doesn't get to the point of having the system loaded and ready to log into. There's no amber lights, just the System LED flashing green fast. On the back, the Power module and all bay lights are green, and the Console light is green, but the Management port light is off.
I've tried using the reset button on the back of the switch two different times to reset it to default configuration, thinking I hosed it somehow, but it never goes past the fast blinking System LED.
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Feb 16, 2013
I have 2 - WS-C2960-24TT-L switches. Both are experiencing the same issue. Upon booting them up, all lights flash on the mode indicator panel, then it goes directly to a solid green "SYST" light. Nothing registers across the console cable. I have tried different baud rates, cables and computers. None of the ports come up regardless of how long either switch is powered on. Holding the Mode button during boot up produces the same result, nothing. Sounds like they are dead, however, I thought this would be the place to go for ideas. Can I revive these switches?
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Dec 5, 2011
I am trying to configure a 3750G that has been sitting on the shelf for several months and am getting the following error -
% Error: Unable to create flash:/microcode_update% Error: It must not already exist
Normally, getting an error during POST isnt a good thing. My first thought was that flash was corrupted or flagged RO somehow. I did fsck flash: with no change. I next tried fsck /test flash:. It tested 77 blocks and performed 0 erasures. It had been running for about 15 minutes with no problems reported so far. Multiple reboots of the switch still report the same error.
I have reviewed the history of what I have done on this switch and finally think I found the problem. I noticed a microcode_update directory that I am not used to see on a 3750. Deleted the directory using the rmdir command and rebooted the switch. On reboot, I noticed that a front_end/ directory was listed as being created as well as fe_type_1 and fe_type_2 were created. The switch now boots up without any errors.
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Dec 8, 2012
I have this routing table which I need to fill in for the network shown in the image attached. guide me to some good resources to understand
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Feb 4, 2013
We have a BGP / OSPF configuration as shown in the topology picture. When the connection towards Internet is taken down, we expect the traffic to be forwarded toward WAN 2 (preferred) or WAN 1. The problem is that the BGP learned routes disappears when the Internet connection is taken down. The IP routing table on R2 only shows internal networks and the networks between R2 and WAN 1 and 2. No routes to internet is shown. We run "show ip bgp neighbors <ip-to-wan-1-router> received-routes" it contain internet routes. And when we run "show ip bgp neighbors <ip-to-wan-1-router> routes" it contains no routes at all.
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Feb 22, 2011
Which data structure used to preparation of a routing table.
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May 9, 2012
I am currently using 2 routers. One is a 2wire router with stock firmware it is connecting to the internet and can't be altered all too much, it also has a PC connected to it. The other is a WRT54GL with Tomato on it with pretty much EVERY other PC and device connected to it, it is also connected to the 2wire and DMZ'd through it.What I want to do is somehow allow everything on the Tomato router to have access to the 2wire router's PC. (For media access or printers or whatever on Windows 7)
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Apr 2, 2013
viewtopic.php?f=33&t=24000
How can you remove these "L" routes in routing table?
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Jul 2, 2012
What are the rough figures that a NPE-G2 is able to hold for the BGP routing table?
378475 network entries using 51472600 bytes of memory 378482 path entries using 21194992 bytes of memory 63008/63003 BGP path/bestpath attribute entries using 8065024 bytes of memory BGP using 82975730 total bytes of memory
Are these 3 memories different memory allocated or are they are a sub-set of each other? If a NPE-G2 has 1GB RAM, does it mean that the routing table limit is depending on the RAM availability?
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May 26, 2013
What is the size of the routing table in the 800 series?
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Jan 9, 2012
today I witnessed a cisco n5k that stopped playing fair. For a yet unkown reason several interfaces started to show output errors all begining within the same second. While i instantly thought this would be a wiring issue I began to ask myself what an output error actually means. Google usually brings up output drops, not regular output errors. So what is it and how can a 10G fiber interface even detect that there is a problem without receiving what it was sending?
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Apr 3, 2012
I have a 3560-24ps, and I'm having issues with it booting. When I power the device up all the front panel lights come on like normail, and then the system light starts flashing like normal, but after 5 - 6 seconds the system light goes off. I don't get any output from the console, and the fans still run.
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Dec 10, 2012
I have a problem on a router of mine, a Quidway R 1760.The problem occurs as follows. On Friday I rebooted the device and the ARP table looked right, in other words there were only a hand fully of lines that looked like this.
[code]...
I have two requests/questions.how can I prevent it.to a software manual for a Quidway R 1760 or simlar? I need to access the routers OS but have no password for it and cannot find any commands on the internet.
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Jan 23, 2011
I need to remove (or change) the default entry in the routing table for Windows XP, which routes packets with a destination equal to the adapter's address to localhost. The reason for this is I want the PC to be able to send packets to a device (with IP address A) connected to one adapter on the PC with IP address B, even though a second adapter on the PC has IP address A.
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Nov 27, 2012
Is there a Table which the list the route table entries on Cisco ISR Router especially ISR 1921 Router.
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Feb 6, 2013
On the 6509, with normal 67xx cards installed, where is all the mac table held, is it held on the card itself or on the supervisor? And if I use dcef cards, I gather the MSFC copies the mac table to the DFC ?
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Jan 11, 2012
Cisco 1812, Version 12.3(8)YI1..What does "none" mean ?Most of mac adressess in cam has specified interface, but several has none.
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Aug 2, 2010
I have quite a few 2960's in a manufacturing environment that are experiencing a large number of Total Output Drops. The gigabit uplinks arn't even close to fully subscribed and if I'm lucky they run at a peak of 4 - 5 Mb on a 1Gb uplink. Something really funky is going on. The individual switchports seem to have the total output drops and the uplinks at 1Gb do not have any output drops and never peak above 20Mb over a 3 month span on a 1Gb link.
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Oct 8, 2012
We are seeing some high output drops on our 3560G's and I'm wondering if there is anything I can do to solve this, or should I just be looking at an upgrade.I do not have qos enabled:
do-rs-ah-3560g#show mls qos
QoS is disabled
QoS ip packet dscp rewrite is enabled
I don't have anything special configured apart from some trunk ports, otherwise its mostly defaults.Should I enable qos and tweak the buffering?
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Jun 4, 2013
We have Cisco Catalyst 6509-V-E VSS Switch with Sup2T und IOS Version 15.0(1)SY2. We are gettin input netflow information from the gi2/3/7 but not output ... I am not sure why it does not work.
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Feb 21, 2012
I have a 3560X that is directly connected to an ASA 5505. I am seeing output drops on the 3560X interface that connects to the ASA. Below are the troubleshooting commands I have ran, but I don't see any indication to what is causing the problem.
3560X
show run int gig 0/24
!
interface GigabitEthernet0/24
[Code]....
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