Network Engineering Stack Exchange
Network Engineering Stack Exchange

Most Popular

more tags
1500 questions
14
votes
2 answers

BGP regular expression .+_.+_.+_.+_.+_.+_.+_.+_.+_.+_.+_.+

could anyone tell me what ip as-path access-list 100 deny .+_.+_.+_.+_.+_.+_.+_.+_.+_.+_.+_.+ stands for?! I searched over the internet for the meaning of this regular expression, but I was unable to find any info.
ipermo
  • 275
  • 2
  • 9
14
votes
3 answers

How does a switch learn a MAC address not in its lookup table?

I have a relatively dumb question. Suppose the Switch just started, and it received a frame that contains a destination MAC address for a network device not in its MAC addresses table. What happens then? Does it broadcast (MAC address…
user24308
14
votes
1 answer

What happened to IPv5?

I hear/read much about IPv4 and IPv6 and nothing about IPv5. Where did it get lost in the discussion?
Waldemar Gałęzinowski
  • 243
  • 1
  • 4
14
votes
2 answers

Does the source MAC address of a frame change when it passes through several switches?

If PC1 sends an Ethernet frame to Switch1 which forwards the frame to Switch2 which in turn forwards the frame to PC2, does any decapsulation happen that changes the source MAC address?
Rana Mallah
  • 175
  • 1
  • 2
  • 6
14
votes
2 answers

In what mode does the 2960-S IOS prompt ends with a colon ":"

QUESTION For a Cisco 2960-S switch, when connecting on the console port, normally the prompt is: SwitchName> then you issue an enable command and end-up with a prompt like: SwitchName# However, I stumbled to diagnostic a switch which was…
Philibert Perusse
  • 345
  • 2
  • 8
14
votes
1 answer

Four layer-2 addresses in 802.11 frame header

I am new to wireless LAN. I see that it has four addresses in the frame header. In case of a Wired Ethernet, there are only two MAC addresses, the source and the destination (which is essentially the address of the next hop). But in case of wireless…
Ankur Bhatia
  • 243
  • 1
  • 2
  • 5
14
votes
6 answers

What happens when the ARP cache overflows?

In at least one implementation there is a hard limit on the capacity of the ARP table. What happens when the ARP cache is full and a packet is offered with a destination (or next-hop) that isn't cached? What happens under the hood, and what is the…
neirbowj
  • 869
  • 1
  • 9
  • 18
14
votes
2 answers

STP blocking port selection

I want to make sure I'm understanding how this works. Specifically the term "Sending Port ID" has me very confused. Consider this diagram, I want to make sure I have root port selection figured out: The switch on top is the root and all settings…
red888
  • 459
  • 1
  • 6
  • 17
14
votes
3 answers

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 service and measure the bandwidth on each vlan. I…
cgasp
  • 2,008
  • 4
  • 21
  • 37
14
votes
2 answers

Stateful vs Stateless IPv6?

What's the difference here? Are stateful IPv6 entries retained in the DHCPv6 server?
stets
  • 1,000
  • 3
  • 8
  • 17
14
votes
3 answers

How does a switch know where to route packet, when there is another switch in front of the destination?

I am just wondering how a switch does know how to route packets to destinations "hidden" behind another switch. In my understanding a switch has a table that maps each of its hardware ports to exactly one MAC-address. So far so good, when a…
Jonas Eschmann
  • 243
  • 1
  • 2
  • 4
14
votes
5 answers

In a multi-tenant environment what should be done to make your switchports silent on Cisco and Juniper switches?

For example preventing it from sending arp, stp, etc and to reveal as little as possible about the rest of the network. Example use case would be connecting to a peering exchange.
SimonJGreen
  • 1,675
  • 12
  • 29
14
votes
1 answer

Under what circumstances are multiple loopback (127/8) addresses useful?

I made an app in java where a client sends ip-packets to a server via the looback-address 127.0.0.1. A really simple app just to test how things work. At first I thought If I created several client-sessions new loppback-hosts would be created. But…
Björn Hallström
  • 287
  • 1
  • 4
  • 11
14
votes
3 answers

how to block ssh tunneling traffic?

if someone were to set up an ssh tunnel to/from work or home, is there a way to prevent future SSH tunneling traffic? I understand that websense can block traffic, but users who use ssh tunneling can bypass websense or other similar products because…
user1609
  • 385
  • 1
  • 4
  • 10
14
votes
3 answers

BGP signalled MPLS issues

I am having an issue getting a VPLS up using an ME3600x with 15.3(2) and BGP signalling. @yelfathi and @packettalk have pointed me down the correct route but not sure how to resolve it. I have 2 ME3600 switches using RSVP as PE and 2 MX80 routers as…
NetDonkey
  • 141
  • 1
  • 6
1 2 3
…
99 100