Cisco Switches :: How To Use SG-300 Combo Ports For Loop Back Testing
Sep 5, 2011
I've got an SG300-10P switch and am trying to use it to create a testing environment for a Fiber Test set. What I would like to do is get two hosts, A & B, plugged into ports 1 and 3 on the switch, to talk to each other, but forcing the traffic to be routed through the two Combo ports 9 & 10. Please see the attached diagram.I've attempted to configure two VLAN's, 10 and 20. Vlan 10 is used for traffic between Ports 1 and 9, Vlan 20 is used for traffic between Ports 3 and 10.I don't really care whether the traffic is tagged or untagged as it passes between ports 9 and 10.
I've tried various combinations of tagged/untagged ports, PVID's, etc. As a first test I've bypassed the Fiber Test set and simply created a direct connection between ports 9 and 10. I am unable to get the traffic from Host A to Host B to get routed through ports 9 and 10 (I ping each host from the other and get no response).
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Aug 12, 2011
What is the purpose of loop back testing.
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Nov 4, 2011
Why is loop-back only working on ports forwarded in the Virtual Server section and not Port Forwarding or even DMZ? I have seen a post about loop-back on the DIR-655 from a while ago that had said to disable SPI and change NAT Endpoint to independent, I have done this and loop-back still doesn't work.
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Jun 7, 2012
I have a bunch of 3750x switches that each have a 10 gig routed link back to a central 4507 (loopback = 172.30.255.255).We carved up a /24 (of course, the /24 doesn't really exist except in our address tracking spreadsheet) into a bunch of /30's for routed WAN links and /32's for loopback addresses.We started on the low end for /30 subnets (ie 172.30.255.0/30, 172.30.255.4/30, etc.).We started at the high end for the /32 loopbacks (ie 172.30.255.255/32, 172.30.255.254/32, etc.)
Well, when I try pinging 172.30.255.255 from the access layer 3750x switches, the 3750x seems to be treating it as a broadcast ping where it lists each member that responds instead of the regular !!!!! response (this makes think something is odd with the 3750x). Of course, only one member responds (the core). But even the core seems to respond with the other end of the /30 instead of the actual /32 loopback (which makes me think something is odd in the core). I could have sworn that I've setup similar topologies without problems (ie, using 10.0.0.0/32, 10.255.255.255/32, etc as loopbacks) and as long as the mask is a /32, it should work.Also, I can ping/ssh to that loopback if my laptop is on a directly connected subnet. But I can't do it from any of the 3750x switches (which are also directly connected).I've double checked for overlapping subnets, but nope. I don't see any. Routing looks fine. The actual /32 is being propagated everywhere properly.
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Mar 19, 2012
I have a Cisco SG300 switch on which trunks are configured. I have a server which sits on the switch via a trunk link of four network cables (4 Gbps total)on which LACP is enabled. I'm having trouble connecting to the server using VNC from a computer on the network. It doesn't happen all the time though, it's just random.
On looking at the logs of the switch, I saw something unusual. The trunk that connects the switch to the server is constantly removing all the member ports and adding them back again after a few minutes interval. That causes the trunk link to flip on and off all the time. What could be the reason that's causing it to happen? I know it could be the network cable but I'm using brand new cables and the server also is brand new.
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Apr 21, 2013
I don't do a lot of networking however during a cisco lesson the other day my lecturer briefly touched upon loop-back tests, would it be okay for somebody to very imply sum up exactly what loop-back tests do in a couple of lines and how they are carried out? (not in detail, so literally for example - a wire is put in from one end of the network to the other etc.) I don't really understand all the different wiring types etc.
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Sep 30, 2011
I recently replaced a client's router with a Cisco RV 120W. The client employs a web-based application on an internal server that manages their business. Workers in the field use a handheld device power by WIndows Mobile to access a mobile version of the the web-based app. Data contained on the mobile app syncronizes with the server when workers choose a sync menu. Some workers perform this sync in the field, others wait till they return to the office and use the wireless provided by the router. Prior to changing the router, the synching worked fine either inside or outside the company network. The mobile app accesses the internal server via the router's public IP address. The router forwards the http requests to the internal server. But now the synching does not work internally. I assume it's because the Cisco RV 120 W does not support NAT Loopback, or I simply haven't figured out how to enable it. Does anyone know how to enable NAT Loopback on the RV 120 W so I can access the web-based app by through the router's external IP while on the private side of the LAN??
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Jul 12, 2011
I am working with a device that does not have a physical reset button on it, and have mistakenly typed in 127.x.x.127 for it's IP. I was trying to use 172, but mistyped and didn't catch it until after I had rebooted the unit. Is there anyway that I might be able to gain access to the device. My PC is running Windows 7, but I am familiar with linux as well. I have attempted to change the loopback adapter IP to 128 on a ubuntu live disc and set my ethernet port to the subnet the device is on with no avail. (I am also using vlans on the device, but believe I have them set up correctly)the device is set to IP: 127.x.x.127 netmask 255.255.255.128. [code] I know that the last octet of 127 is the broadcast IP for the range, but have been able to address similar blunders before by forcing myself to a /24 subnet to correct that.
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May 7, 2012
I am terminating GRE vrf-lite on my 7600 and using loopback as source for each client.I found one problem where 7600 seems to be not forwarding traffic until I delete create the tunnel interface.Worked fine for a week. Then stopped again. I had to delete,create again tunnel interface.
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Jan 12, 2013
We have 6 WAN routers connected through ISP MPLS cloud , we need to implement GET VPN between these WAN routers.We have 2 Key servers (1800 routers) , and the WAN routers will act as Group Members (6 GMs)
The attached configuration files are for working configuration for typical GETVPN (crypto map applied on WAN interface)
In Key server configuration , the crypto isakmp command is using the WAN interface IP address of each WAN router (172.16.x.x) , and since that the KS routers are connected to local backbone (VSS) , they should be able to reach 172.16.X.X , and therefore the subnet 172.16.X.X is advertised to the local network (check GM configuration file under eigrp - redist connected )
This is what our customer want to avoid ! they do not want 172.16.X.X to be advertised to the local network .I know It is possible in GETVPN configuration to configure ,the crypto isakmp command to use loopback address's of the WAN routers instead of the WAN IP , but in this case the crypto map must be applied to the loopback address , and this requires all traffic to be encrypted and decrypted to go through the loopback interfaces on all WAN routers .
i was wondering what is the best solution for this case , I though to use the below config on the GM's
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Feb 19, 2013
I need to NAT a port range spanning from TCP and UDP 50,000 to 59,999 from inside global address 58.96.x.x on loopback2 to an inside local address of 192.168.5.5.Currently all the existing NAT translations are 1-to-1 that map inside global addresses on a wide span of Loopbacks and a Dialer Interface to inside local addresses on few subnets which are fine.I'm using an 1811 with an ADVIPSERVICESK9-M image, version 12.4(6)TS
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Nov 22, 2012
I am having a hard time trying to configure DMVPN with the tunnel being sourced via a loopback interface. All routers are Cisco 886 routers which don't have L3 ports.That is why I used SVI interfaces, and have configured the L2 ports (Fa0, Fa1, etc.) with the command switchport access vlan.The problem is that I am receiving Invalid SPI error's only on the Hub router and I have no clue what could be the problem, because they use exactly the same parameters for IPsec. [code]
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Jul 4, 2012
How to create loopback cable for gig copper port (cisco 6513).I
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Nov 17, 2012
I have a couple a questions answers on which i cant google for a period. BTW maybe i simly use wrong aproach to choose keywords.
1) Is it possible to assign same ip address to the same client each time it authenticated, preferably without using DHCP? Im definely sure that it possible but cant find corresponded configuration examples (my device is Cisco 1921 with IOS 15.0.1).
2) Is it possible to assign dynamic crypto map to loopback interface (the purpose to make EASY VPN Server accessible through two interfaces - maybe you recommend other approach instead?) - as i move workingcrypto map from phy int to loopback - i cant connect with reason "Phace1 SA policy proposal not accepted"
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Aug 18, 2012
The following error was seen on the switch and the Diagnostic Test Loop back failed following a new WS-6748-SFP module installation.Fabric in slot 5 detected excessive flow-control on channel 3 (Module 4, fabric connection 1)
Tried Hard reset of the module and still the error persist.
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Apr 6, 2012
Here is my Lab Setup: 2691 is BGP nei to R4 router and they are not directly connected. 2691 and R4 are in same AS 6500. 2691 Config---router ospf 1 network 3.3.3.3 0.0.0.0 area 0 . Its advertising its loop back IP to OSPF domain.
router bgp 6500
no synchronization
bgp log-neighbor-changes
neighbor 6.6.6.6 remote-as 6500
neighbor 6.6.6.6 update-source Loopback3
[code]...
R4 Router
router ospf 11
log-adjacency-changes
network 6.6.6.6 0.0.0.0 area 0
[ code].....
We can see that 2691 and R4 are BGP neis and 2691 has 200.1.x.x routes in its route table. My question is why from 2691 router i am unable to ping any route learned by BGP from R4?
2691Router# ping 50.1.1.0 Type escape sequence to abort.Sending 5, 100-byte ICMP Echos to 50.1.1.0, timeout is 2 seconds:.....Success rate is 0 percent (0/5)2691Router#ping 200.1.2.0 [ code]...
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Sep 14, 2012
I am trying to configure a loop back interface like so: [URL], on the following device:
C3550 Software (C3550-IPSERVICESK9-M), Version 12.2(50)SE, RELEASE SOFTWARE (fc1on port gig0/1 which is using a 1000Base-SX adapter. This is for troubleshooting purposes and it does not appear to be a feasible option. Is there another way to accomplish in the IOS?
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Jan 16, 2011
is it possible to assign a loopback address to a typical switch port on a 2950 switch? I want to be able to have some devices connected to a switch to test access lists and VLANs.
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Dec 27, 2012
All my switches were connected together as ring topology. We use REP to block redundancy link.One of my colleagure was setting up a new link(VLAN) for one customer which was then caused a L2 loop. The CPU was hitting 100% and REP started to lost neighbors then we had a big outage.I am thinking to deploy QoS on all REP switch (on trunk links from switch to switch) to give priority to control traffic like REP and some importance data VLAN. Of course,Storm-Control already implemented on all access-port.
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Aug 23, 2011
My Motorola SBG901 Modem/Router combo has stopped connecting to the internet. I have done all the troubleshooting with Comcast and with Motorola and it is out of warranty, so I will have to purchase a new one.In the mean time, I wanted to use it only as a wireless router connected to my Scientific Atlanta DPC2100R2 modem. Is there anyway to do this? Is there a way to disable the modem in the SBG901? Simply connecting with the ethernet cords has not worked. I connected the DPC2100 to the SBG901 via ethernet cord. My computer was able to pick up a wireless connection but there is no cable connection.
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Aug 9, 2011
My SG300-52 is struck in reboot loop after i set tcp congestion avoidance in webui.
********************************************
Boot1 Checksum Test...............................PASS
Boot2 Checksum Test...............................PASS
Flash Image Validation Test.......................PASS
[code]....
i've tried flashing new firmware via xmodem but still have problem.
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Nov 24, 2012
We have a couple of cisco SGE switches connected to a single DELL, between the cisco switches we have a trunk interface. I'm not sure which setting should be configured on the switches to get it working because a loop is occuring.
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Jun 22, 2012
After performing a firmware upgrade on an SG300-20 switch from ver 1.1.0.73 to 1.2.5.70 the switch now boots up with the following error and resets:
30-Aug-2011 10:47:33 %L1Mngr-F-PARAMTOOLONG: csco-sb parameter %s is too long.
The attached file contains a full output of the console boot process. I have tried loading different versions from the console, but all produce the same error.
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Sep 12, 2012
So the SG300's have STP on them and prevent network loops when other switches on the network also support STP too. However, if someone plugs in a non-managed switch that doesn't support STP with a network loop, is there anything within the SG300 switches to isolate and/or prevent that from happening?
(I currently have port mirroring turned on for one port and a network sniffer attached awaiting the incident to happen again).
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May 2, 2012
i have recently tried to change the catos on a Catalyst 2948G-L3 and since then i have the following message in a loop : [code] I know that the solution would be to download a new valid image from tftp via the common prompt but what i don't undertand is why i cant access the rommon prompt.
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Nov 7, 2012
I have a couple of 3560 switches running c3560-advipservicesk9-mz.122-44 and they are randomly experiencing the following:
- The switch locks up with no preceding error message in the log (I am forwarding syslog to Splunk).
- Upon reboot, the switch goes through the normal startup sequence with no error messages, then for some reason reloads the flash and starts all over again. (refer to doc)
This could happen after days or weeks. Sometimes they will go through two of these reloads on boot and be fine for awhile, and other times they will be stuck in the loop infinitely. I am using this same image with all of our 3560s, but am only having this issue with two of them.
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Feb 5, 2013
We have a Cisco 3750G Core switch which has physical connections, each configured as trunks to two HP Access switches. The client who uses these access switches would like to put a link between the two, but this would create a loop.
------- Core Switch -------
| |
| |
[Code]....
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Dec 18, 2011
How can i get information about the back plane utilization. is there any command for the SB-switches (sg300).
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Feb 15, 2012
I looking to buy SGE 2010 swith, but I have some question:
1. Can I use 4 SFP ports and stack of two switches at the same time.
2. Is it possible to use for stacking ports other than 24, 48?
3. What is maximum possible number of ports to use for stacking (can I get more than 1Gb thruput).
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May 31, 2011
On my Cisco SLM248G Switch the Back pressure and Flow control are currently disable.For the Flow control is it best to set it to enable or just Auto negotations and for the Back pressure is it ok the Enable it.This Cisco Switch has 3 servers and 15 laptop users connected to the ports.Will there be a draw back to enable these settings.
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Nov 25, 2012
I have a Cisco 8510msr that is connected back to back with a 7206vxr across a 155Meg connection.I receive lots of Output drops on the 7206vxr interface facing the atm switch. When I do the following command:-
kwdair9#sh atm int atm 1/0Interface ATM1/0:AAL enabled: AAL5 , Maximum VCs: 4096, Current VCCs: 27 Maximum Transmit Channels: 0Max. Datagram Size: 4528PLIM Type: SONET - 155000Kbps, TX clocking: LINECell-payload scrambling: ONsts-stream scrambling: ON797522 input, 881483 output, 203946630 IN fast, 223768062 OUT fast, 0 out dropVBR-NRT : 110288 Avail bw = 44712 <====
I only have 44megConfig. is ACTIVEkwdair9# I only get 44Meg of the available 155Meg.There is no QOS on the router and the only commands I can find that vaguely see that refer to QOS are on the ATM switch:-
atm address 47.0091.8100.0000.0007.0d87.b201.0007.0d87.b201.00atm router pnnino aesa embedded-number left-justifiednode 1 level 56 lowest redistribute atm-static?why this is acting like a DS3 link and not a 155Meg link?
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Dec 4, 2011
What cable I need to connect two 2951 back to back through a HWIC-4T1/E1 card ?
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Apr 11, 2013
I have two site that has a copper wire ( 2 wire) connection between each router ( No Telco in between ). Now I want to use 1921 router with HWIC-4SHDSL-E card to connect these two site together. Can I use attach configuration to make the connection reference from the diagram ?
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