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PPPoA ADSL Configuration with external modem on Cisco 891

Context We use Cisco 891 routers as CPE for several client sites. They are all running IOS 15. Cisco IOS Software, C890 Software (C890-UNIVERSALK9-M), Version 15.0(1)M8, RELEASE SOFTWARE (fc1) The majority of these sites terminate against an…
Geekman
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Is CIDR IP format currently in use?

I'm reading a book that says that, historically, there have been three ways to interpret IP addresses: Classful Subnetting with subnet masks Classless Inter-Domain Routing(CIDR), supernetting. My question is: If CIDR is in use, why I never see IPs…
What Else
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why STUN doesn't work with symmetric NAT?

I read this line from wikipedia. "STUN does work with three types of NAT: full cone NAT, restricted cone NAT, and port restricted cone NAT. In the cases of restricted cone or port restricted cone NATs, the client must send out a packet to the…
Kristen
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Port mirroring just the Rx (or Tx) direction of a port?

Something on my Ethernet LAN is occasionally sending out spurious duplicate packets and I need to track it down. The culprit is likely a switch or other bridge (such as a Wi-Fi AP) and not an endpoint, because the packets that get duplicated are not…
Spiff
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Where are 0 TCP/UDP ports banned?

It is well-known that, on most systems, using 0 for the UDP destination port or for the TCP source or destination ports is disallowed. Is this required by RFCs, or is this just common practice? If it's required, which RFCs require it?
joshlf
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4 answers

speed/duplex mismatch

How do mismatches occur; what is the impact of a mismatch on network connectivity; is resolution of mismatches really worth the effort; what are some ways to detect mismatches on a large scale?
Dennis Olvany
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Why does PPP need an underlying protocol?

The Point-to-Point Protocol is (at least according to Wikipedia) a Datalink Layer Protocol. I know that different use cases exist for it but on examining the image below from Wikipedia one can see that it always seems to need a wrapping protocol…
Martin Dallinger
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3 answers

Spanning tree Default Priority Values

This question is a repost of the same question in The Cisco Learning Network; however, the answers are unique to Stack Exchange. I have always accepted that the defualt priority value of STP (802.1d) is 32768 (32768 + sys-id-ext x) as show in "show…
Trojan
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Does the destination port change during TCP three-way handshake?

I'm learning networking programming in C and there is a question bothers me a lot, does the destination port change during TCP three-way handshake? Let's say I have a cilent application running on port 5000 and a web server running on tcp port…
secondimage
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How do load balancers fit in to a data center with much higher throughput than they can handle?

You have a data center standardized on 10GE connections. With, say, Nexus 7000s in the core, Nexus 5000s at the aggregation, and some fabric extenders for the edge to the servers (I use Cisco gear as examples because this is what's in my specific…
sentinel
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3 answers

Oversubscription in cisco 6500

What is oversubscription?When selecting a 16 port 10 gig blade for cisco 6500 , it says oversubscription as 4:1. What will happen if I populate all 16 ports, will some ports be blocking or dropping packet?
NAVEEN GEORGE
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WHY and HOW do routers and vlans break broadcast domains?

Everybody says routers (and vlans) break broadcast domains, but nobody goes into WHY that is, it seems. What's the router logic? Say I have three routers on my lan, with one main router and the other two merely bridged to the first (not creating…
Daniel
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Will ASA 5540 support 3000 simultaneous IPsec connections?

As part of a new project, we have a requirement to terminate about 3000 IPsec connections on a Cisco ASA 5540 firewall. According to the specs, the maximum IPsec Peers this platform supports is 5000 so there shouldn't be a problem. The question is…
Stefan Radovanovici
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Strange drop-outs in Cisco 7200 LNS lab

I'm testing several functions on emulated Cisco 7200 routers, in GNS3, prior to actual purchase. One of the functions I've been testing out is LNS functionality. I've been primarily following this blog post in terms of my topology and configuration,…
Geekman
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6 answers

Is policy routing bad?

I heard that network engineers tend to avoid policy routing. I am thinking to source-address dependent routing for example. Is policy routing bad practice? If so, why?
exeral
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