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33

The MTU is the Maximum IP packet size for a given link. Packets bigger than the MTU is fragmented at the point where the lower MTU is found and reassembled further down the chain. If no fragmentation is wanted, either you have to check the MTU at each hop or use a helper protocol for that (Path MTU Discovery). Note that IPv6 does NOT support packet ...


23

In addition, MSS value is derived from the MTU. Consider that you have data of 2260 bytes to be sent to a remote device. If MTU is 1500, and we consider IP header + TCP header to be 40 bytes, then only 1460 bytes of data can be sent in the first IP packet. The remaining 800 bytes will be sent in the second IP packet. So, for MSS = 800, the MTU should be at ...


20

You might care to read RFC 1547 "Requirements for an Internet Standard Point-to-Point Protocol" which explains how the PPP was chosen. The thing I'd suggest you are missing is that interoperability is one of the principal driving forces in the internet protocols, and efficiency is much less important. You do the highly talented engineers who designed PPP a ...


16

Why does PPP need a wrapping protocol? PPP is not a layer-1 protocol, so it needs a layer-1 protocol to carry it. Protocols like ethernet are both layer-1 and layer-2 protocols, so PPP can use ethernet as its layer-1 protocol, but that comes with the ethernet layer-2 protocol that wraps PPP. Why can't I just use PPP over Ethernet instead of PPPoE? PPPoE ...


12

Another reason may be that PPPoE is a tunnelling protocol which is useful for security and hiding an ISPs infrastructure. A tunnel is created between the end user CPE and ISP’s centralised BRAS. The network in-between is hidden from the user and the user cannot interact with other users directly over the ISP’s distribution network until it reaches the BRAS ...


11

So in the strictest sense, "IP over Ethernet" is exactly what it sounds like, it's the encapsulation of IP packets (datagrams, formally) in standard ethernet frames. For much of the networking universe this is just "normal" IP as so much of the transport has migrated to Ethernet nowadays. Somewhat more specifically speaking, IPoE is often used in ...


11

PPP is designed to ride on top of a byte-oriented, point-to-point physical-layer protocol like a simple modem-style serial link. Ethernet is no simple serial protocol but it requires frame-level addressing (L2 MAC address), so PPPoE expands standard PPP to take care of discovery and addressing between the link partners.


10

Is ADSL's UDP packet forwarding rate strictly linear to packet size? The answer is "no, because of the variable nature of ATM AAL5 padding used in ADSL lines". Since you aren't sure what encapsulation is used on the ADSL modem, I'll assume it's PPPoE, most providers use PPPoE for customer connections. I also assume that you've measured the full ATM ...


9

A few reasons. Firstly that is just the way it has always been and ISPs are loath to change a working setup. Secondly it's possible to create translators between different types of PPP. Just because what your router sees is PPPoE doesn't mean the path all the way back to your ISP is a simple ethernet network. You might have a setup that is PPPoE from your ...


9

IPoE is essentially DHCP-triggered subscriber interfaces. It has come about because most modern broadband access networks are able to deliver Ethernet from end-to-end (e.g.: xPON/FTTH). Users are "authenticated" through the use of DHCPv4/v6 Option-82 inserting their Circuit-ID into their initial DHCP Discovery - this identifies the physical location of the ...


8

The most and noticeable different is layer of tunneling. PPPOE is a Layer 2 (Data Link Layer) tunneling protocol while L2TP is a Layer 3 (Network Layer) tunneling protocol. This means that PPPOE can create a tunnel between devices in a broadcast domain (such as devices connect to the same switch) but L2TP can create a tunnel between two IP-based device ...


7

PPTP, PPPoE, and L2TP all provide OSI Layer 2 services. That is, the user of these protocols (usually, a network layer protocol suite) thinks it's running over a "normal" link layer. However, each of these protocols provides the link layer service by transporting packets over another service, rather than over the physical layer. PPTP provides ...


7

NAT is applied to g0/0, not di0 where it is required. (there's no IP running on g0/0, so none of the IP configuration matters there.) int di0 ip nat outside ! no ip nat inside source list 1 interface GigabitEthernet0/1 overload ip nat inside source list 1 interface di0 overload The two route statements are not necessary. If you need something to trigger ...


7

Yes, the "E" in PPPoE stands for ethernet. The PPP stands for Point-to-Point Protocol. PPPoE and PPPoA are often used with DSL. PPP was the original protocol which was allowed by the DSL Forum. PPP provides more options and security for the ISP than does DHCP. For instance, DHCP offers no authentication, but that is built into of PPP. Juniper has a ...


6

*cough* interface Dialer0 ip nat outside


6

PPP doesn't use MAC addresses or ARP the way ethernet does, so no, there will not be ARP in PPP, but there may be ARP in the ethernet which carries the PPP frames. You will not see anything ethernet-related in the PPP. What you are looking at is the PPP, not the ethernet. ARP (Address Resolution Protocol) is used by some layer-2 protocols, e.g. ethernet, to ...


6

If I have a switch or laptop running a PPPOE server, could I go from ethernet-to-modem then connect the modem's WAN port to another modem's WAN port and have it connect via PPPOE? No. A DSL modem is the CPE part of a DSL link. You can't connect two CPEs, only CPE to COE, e.g. a DSLAM. DSLAMs usually require substantial infrastructure, so a lab environment ...


5

The NAT statement ip nat inside source list 1 interface GigabitEthernet0/1 overload is incorrect. You should specify the dialer0 interface instead. Here's a helpful link. http://www.cisco.com/en/US/docs/routers/access/800/850/software/configuration/guide/pppoenat.html#wp1235296


5

You are missing a critical NAT command. Try adding ip nat outside under the outbound dialer interface interface Dialer 0. With your current configuration you've identified the interface Gig 0/1 as the "Inside" interface, so the router knows when to apply NAT rules to the incoming traffic on that interface. However, since the Dialer 0 interface does not ...


5

I'd remove the Ericsson box. It isn't a BRAS. From your diagram it looks like you'd be using it as a aggregation switch and the Linux PPP Server would be your BRAS. Personally, for lab purposes I'd also remove the Linux PPP Server and hook the DSLAM up to a Cisco 3825 or 7200 configured as a BRAS. If you really want the Linux element set up a FreeRADIUS ...


5

The first diagram will not work, and in fact may result in damage to your router. The AUX port is a regular RS232 serial port, which is completely incompatible with ADSL. Don't do it. The second diagram should work, provided your D-Link modem can operate in bridged mode.


5

In this case, your router talks PPP to the provider directly. But first, the router puts this data into Ethernet frames which it transmits to the modem. (hence PPP-over-Ethernet) Since the modem is in bridge-mode, it won't interpret the frames, only encapsulate them itself in AAL (ATM Adaption Layer) or whatever in order to transmit over the public network ...


5

According to Cisco, you cannot use DHCP with PPPoE, : PPPoE is not supported in conjunction with DHCP because with PPPoE the IP address is assigned by PPP. Juniper has a whitepaper about Understanding PPPoE and DHCP: The DSL Forum now also allows using IP over Ethernet (IPoE), which is based on DHCP. However, PPP remains the more mature and robust method ...


5

( As others have already said, PPPoE is literally PPP over Ethernet. And similarly PPPoA is PPP over ATM. ) Ethernet and ATM are oddities in the networking world as they define both a layer-1 and layer-2 component. In the case of ethernet, it's layer-1 has always used it's layer-2; no one ever built it any other way. (Ethernet's layer-2 protocol, however, ...


4

Testing that kind of features using GNS3 is simply waste of time. You're emulating at run-time complex software, and on top of that, you're adding complex features. There's no sense in 'trying' 7200 as 7200 are long EoS: http://www.cisco.com/c/en/us/products/collateral/routers/7200-series-routers/end_of_life_c51-681414.html Download CSR 1000v and test in ...


4

Adding to the other answers... the thing you lack now is an access-list to limit NAT to your inside addresses... if you apply this configuration, I think this should get you going as long as there aren't other subnets routed by this router. ! interface GigabitEthernet0/1 ip address 192.168.2.1 255.255.255.0 ip nat inside interface Dialer0 ip nat ...


4

For your home router to establish a WAN connection to your ISP, a few things specific to PPP must happen first. You may also have to do some research on LCP and NCP. Check this link below, it may have the answer you are looking for (see the excerpt on PPPoE below): https://infoproducts.alcatel-lucent.com/html/0_add-h-f/93-0098-09-01/...


4

I think what you want to set is the interface MTU not the ip MTU. Just use this command and you will be good to go: mtu 1492 But the ppp mtu adaptive is usually the way to go


4

Except the 1750 only has one fastethernet port. A WIC-1ENET is 10m, WIC-4ESW a 4 port switch... but they both live on the WIC bus that'll top out about 6-8m. Depending on your DSL speed, this may not be a problem. I use a WIC-1ADSL (and WIC-4ESW) in a 1720, but the DSL line is 6m anyway. (and neither the 1720 nor 1750 support dot1q; that's a feature of ...


4

Can you explain what happens to the frames tagged 100 as they go through (or try to go through) this Gi0/0/0.1 sub-interface? First, let's be a little more clear about your configuration for other readers. More than likely, you also have an interface in the router configured like this: interface Dialer1 mtu 1492 ip address negotiated ip nat outside ip ...


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