[rlug] Re: problema: tunnel & NAT

[Alin Nastac]

Emil Buliga wrote:

Acum revenind la problema. Nu exista alta solutie decit cea care ti-am zis-o.
Daca tu stii alta solutie decit a manglui MSS-ul pt conexiunile TCP, te rog sa o expui.Nu ma refer la nu-stiu-ce-echipamente care in fond tot asta fac.

Printre solutiile realiste:
1.Use a proxy-server (or, even better, a Web cache engine) between R2 and
the Gateway router, and let the proxy-server request all the Internet pages.

Asta nu e o solutie. Doar nu reducem totul la web, nu?

2. If the GRE tunnel runs over links that can have an MTU greater than 1500
bytes plus the tunnel header, then another solution is to increase the MTU
to 1524 (1500 plus 24 for the GRE overhead) on all interfaces and links
between the GRE endpoint routers.

Iarasi nu e o solutie, de vreme ce link-urile care le-am vazut io pina acum nu au avut MTU > 1500.

3. (Use policy routing to) clear and set the DF bit in the data IP packet.
Cred ca e posibil si in linux - nu am studiat varianta asta.

Nu cred ca ar fi normal sa resetezi bitul asta de vreme ce capetele respectivelor conexiuni nu vor sa primeasca pachete fragmentate. Normal ar fi sa refuze sa primeasca asa ceva, de vreme ce nu isi aloca memoria suplimentara necesara defragmentarii.

5.A final option is to increase the IP MTU on the tunnel interface to 1500.
However, increasing the tunnel IP MTU
causes the tunnel packets to be fragmented because the DF bit of the
original packet is not copied to the tunnel packet header. In this scenario,
the router on the other end of the GRE tunnel must reassemble the GRE tunnel
packet before it can remove the GRE header and forward the inner packet. IP
packet reassembly is done in process-switch mode and uses memory. Therefore,
this option can significantly reduce the packet throughput through the GRE
tunnel.

Ar fi posibil da' inseamna o serioasa scadere a performantei. Gindeste-te ce throughput poti sa ai daca la cele doua capete se reasambleaza un pachet de 1500 octeti format din 2 pachete (ultimul avind o dimensiune neglijabila). Nemaivorbind de memoria suplimentara necesara reasamblarii pachetelor.

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